Lumen design for catheter

ABSTRACT

The invention provides a device for heating or cooling a surrounding fluid in a feeding vessel and a method of manufacturing the same. The device includes a catheter assembly capable of insertion to a selected blood vessel in the vascular system of a patient. The assembly includes an elongated catheter body, a heat transfer element located at a distal portion of the catheter body and including an interior, an elongated supply lumen adapted to deliver a working fluid to the interior of the heat transfer element and having a hydraulic diameter, an elongated return lumen adapted to return a working fluid from the interior of the heat transfer element and having a hydraulic diameter, and wherein the ratio of the hydraulic diameter of the return lumen to the hydraulic diameter of the supply lumen is substantially equal to 0.75. The method of manufacturing the catheter assembly involves extruding an elongated catheter body; locating a heat transfer element including an interior at a distal portion of the catheter body; extruding an integrated elongated bi-lumen member including a first lumen adapted to receive a guide wire and a second lumen having a hydraulic diameter, the second lumen comprising either a supply lumen to deliver a working fluid to an interior of the heat transfer element or a return lumen to return a working fluid from the interior of the heat transfer element; and providing the integrated bi-lumen member substantially within the elongated catheter body so that a third lumen having a hydraulic diameter is formed, the third lumen comprising either a supply lumen to deliver a working fluid to an interior of the heat transfer element or a return lumen to return a working fluid from the interior of the heat transfer element and the ratio of the second lumen hydraulic diameter to the third lumen hydraulic diameter is substantially equal to 0.75.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to lumen designs for catheters.More particularly, the invention relates to lumen designs for cathetersthat modify and control the temperature of a selected body organ.

2. Background Information

Organs in the human body, such as the brain, kidney and heart, aremaintained at a constant temperature of approximately 37° C. Hypothermiacan be clinically defined as a core body temperature of 35° C. or less.Hypothermia is sometimes characterized further according to itsseverity. A body core temperature in the range of 33° C. to 35° C. isdescribed as mild hypothermia. A body temperature of 28° C. to 32° C. isdescribed as moderate hypothermia. A body core temperature in the rangeof 24° C. to 28° C. is described as severe hypothermia.

Hypothermia is uniquely effective in reducing brain injury caused by avariety of neurological insults and may eventually play an importantrole in emergency brain resuscitation. Experimental evidence hasdemonstrated that cerebral cooling improves outcome after globalischemia, focal ischemia, or traumatic brain injury. For this reason,hypothermia may be induced in order to reduce the effect of certainbodily injuries to the brain as well as other organs.

Cerebral hypothermia has traditionally been accomplished through wholebody cooling to create a condition of total body hypothermia in therange of 20° C. to 30° C.

Catheters have been developed which are inserted into the bloodstream ofthe patient in order to induce total body hypothermia. For example, U.S.Pat. No. 3,425,419 to Dato describes a method and apparatus of loweringand raising the temperature of the human body. Dato induces moderatehypothermia in a patient using a metallic catheter. The metalliccatheter has an inner passageway through which a fluid, such as water,can be circulated. The catheter is inserted through the femoral vein andthen through the inferior vena cava as far as the right atrium and thesuperior vena cava. The Dato catheter has an elongated cylindrical shapeand is constructed from stainless steel. By way of example, Datosuggests the use of a catheter approximately 70 cm in length andapproximately 6 mm in diameter.

Due to certain problems sometimes associated with total bodyhypothermia, attempts have been made to provide more selective cooling.For example, cooling helmets or headgear have been used in an attempt tocool only the head rather than the patient's entire body. However, suchmethods rely on conductive heat transfer through the skull and into thebrain. One drawback of using conductive heat transfer is that theprocess of reducing the temperature of the brain is prolonged. Also, itis difficult to precisely control the temperature of the brain whenusing conduction due to the temperature gradient that must beestablished externally in order to sufficiently lower the internaltemperature. In addition, when using conduction to cool the brain, theface of the patient is also subjected to severe hypothermia, increasingdiscomfort and the likelihood of negative side effects. It is known thatprofound cooling of the face can cause similar cardiovascular sideeffects as total body cooling. From a practical standpoint, such devicesare cumbersome and may make continued treatment of the patient difficultor impossible.

Selected organ hypothermia has been accomplished using extracorporealperfusion, as detailed by Arthur E. Schwartz, M.D. et al., in IsolatedCerebral Hypothermia by Single Carotid Artery Perfusion ofExtracorporeally Cooled Blood in Baboons, which appeared in Vol. 39, No.3, Neurosurgery 577 (September, 1996). In this study, blood wascontinually withdrawn from baboons through the femoral artery. The bloodwas cooled by a water bath and then infused through a common carotidartery with its external branches occluded. Using this method, normalheart rhythm, systemic arterial blood pressure and arterial blood gasvalues were maintained during the hypothermia. This study showed thatthe brain could be selectively cooled to temperatures of 20° C. withoutreducing the temperature of the entire body. However, externalcirculation of blood is not a practical approach for treating humansbecause the risk of infection, need for anticoagulation, and risk ofbleeding is too great. Further, this method requires cannulation of twovessels making it more cumbersome to perform particularly in emergencysettings. Even more, percutaneous cannulation of the carotid artery isdifficult and potentially fatal due to the associated arterial walltrauma. Finally, this method would be ineffective to cool other organs,such as the kidneys, because the feeding arteries cannot be directlycannulated percutaneously.

Selective organ hypothermia has also been attempted by perfusion of acold solution such as saline or perflourocarbons. This process iscommonly used to protect the heart during heart surgery and is referredto as cardioplegia. Perfusion of a cold solution has a number ofdrawbacks, including a limited time of administration due to excessivevolume accumulation, cost, and inconvenience of maintaining theperfusate and lack of effectiveness due to the temperature dilution fromthe blood. Temperature dilution by the blood is a particular problem inhigh blood flow organs such as the brain.

Catheters adapted for delivering heat transfer fluids at temperaturesabove or below normal body temperatures to selected internal body siteshave been devised in the past (See, for example, U.S. Pat. No. 5,624,392to Saab). These catheters often have a concentric, coaxial configurationof multiple lumens. The configurations often have a first central lumenadapted to receive a guide surrounded by a concentric second supplylumen adapted to supply a working fluid to a distal portion of thecatheter and an outer concentric third return lumen, which surrounds thesecond lumen, adapted to return a working fluid to a fluid source. Aproblem with this configuration is that the working fluid in the supplylumen makes surface area contact with both an outer wall, whichpartially defines the outer limits of the second lumen, and an innerwall, which defines the first lumen, leading to increased heat transferbetween the walls and the working fluid. Thus, if the second supplylumen in the catheter is designed to deliver a cooling fluid to thedistal portion of the catheter, the increased surface area contactcaused by this configuration unnecessarily warms the cooling fluid priorto delivery to the distal portion of the catheter. Another problem withthese catheters is that the supply lumen(s) and return lumen(s) are notsized relative to each other to maximize the flow rate through thecatheter. Hence, they do not optimize heating and/or cooling catheterperformance.

BRIEF SUMMARY OF THE INVENTION

The present invention involves a device for heating or cooling asurrounding fluid in a blood vessel that addresses and solves theproblems discussed above with multiple lumen arrangements of cathetersin the past. The device includes an elongated catheter body, a heattransfer element located at a distal portion of the catheter body andincluding an interior, an elongated supply lumen adapted to deliver aworking fluid to the interior of the heat transfer element and having ahydraulic diameter, an elongated return lumen adapted to return aworking fluid from the interior of the heat transfer element and havinga hydraulic diameter, and wherein the ratio of the hydraulic diameter ofthe return lumen to the hydraulic diameter of the supply lumen issubstantially equal to 0.75.

Implementations of the above aspect of the invention may include one ormore of the following. The supply lumen may be disposed substantiallywithin the return lumen. One of the supply lumen and return lumen mayhave a cross-sectional shape that is substantially luniform. One of thesupply lumen and the return lumen has a cross-sectional shape that issubstantially annular. The supply lumen has a general cross-sectionalshape and the return lumen has a general cross-sectional shape differentfrom the general cross-sectional shape of the supply lumen. The catheterassembly includes an integrated elongated bi-lumen member having a firstlumen adapted to receive a guide wire and a second lumen comprisingeither the supply lumen or the return lumen. The bi-lumen member has across-sectional shape that is substantially in the shape of a figureeight. The first lumen has a cross-sectional shape that is substantiallycircular and the second lumen has a cross-sectional shape that issubstantially annular. The heat transfer element includes means forinducing mixing in a surrounding fluid. The device further includesmeans for inducing wall jets or means for further enhancing mixing ofthe working fluid to effect further heat transfer between the heattransfer element and working fluid. The heat transfer element includesan interior distal portion and the supply lumen includes first means fordelivering working fluid to the interior distal portion of the heattransfer element and second means for delivering working fluid to theinterior of the heat transfer element at one or more points pointproximal to the distal portion of the heat transfer element.

A second aspect of the invention involves a catheter assembly capable ofinsertion into a selected blood vessel in the vascular system of apatient. The catheter assembly includes an elongated catheter bodyincluding an operative element having an interior at a distal portion ofthe catheter body, an elongated supply lumen adapted to deliver aworking fluid to the interior of the distal portion and having ahydraulic diameter, an elongated return lumen adapted to return aworking fluid from the interior of the operative element and having ahydraulic diameter, and wherein the ratio of the hydraulic diameter ofthe return lumen to the hydraulic diameter of the supply lumen beingsubstantially equal to 0.75.

Any of the implementations described above with respect to the firstaspect of the invention also apply to the second aspect of theinvention. Further, implementations of the second aspect of theinvention may include one or more of the following. The operativeelement may include a heat transfer element adapted to transfer heat toor from the working fluid. The heat transfer element may include meansfor inducing mixing in a surrounding fluid. The operative element mayinclude a catheter balloon adapted to be inflated with the workingfluid.

A third aspect of the invention involves a device for heating or coolinga surrounding fluid in a vascular blood vessel. The device includes anelongated catheter body, a heat transfer element located at a distalportion of the catheter body and including an interior, an integratedelongated bi-lumen member located within the catheter body and includinga first lumen adapted to receive a guide wire and a second lumen, thesecond lumen comprising either a supply lumen to deliver a working fluidto an interior of the heat transfer element or a return lumen to returna working fluid from the interior of the heat transfer element, and athird lumen comprising either a supply lumen to deliver a working fluidto an interior of the heat transfer element or a return lumen to returna working fluid from the interior of the heat transfer element.

Implementations of the third aspect of the invention may include one ormore of the following. The catheter body includes an internal wall andthe integrated bi-lumen member includes an exterior wall, and the thirdlumen is substantially defined by the internal wall of the catheter bodyand the exterior wall of the bi-lumen member. Both the catheter body andthe bi-lumen member are extruded. The bi-lumen member is disposedsubstantially within the third lumen. The second lumen has across-sectional shape that is substantially luniform. The third lumenhas a cross-sectional shape that is substantially annular. The secondlumen has a general cross-sectional shape and the third lumen has ageneral cross-sectional shape different from the general cross-sectionalshape of the second lumen. The bi-lumen member has a cross-sectionalshape that is substantially in the shape of a figure eight. The firstlumen has a cross-sectional shape that is substantially circular and thesecond lumen has a cross-sectional shape that is substantially luniform.The heat transfer element includes means for inducing mixing in asurrounding fluid. The device further includes means for inducing walljets or means for further enhancing mixing of the working fluid toeffect further heat transfer between the heat transfer element andworking fluid. The heat transfer element includes an interior distalportion and the supply lumen includes first means for delivering workingfluid to the interior distal portion of the heat transfer element andsecond means for delivering working fluid to the interior of the heattransfer element at one or more points point proximal to the distalportion of the heat transfer element.

A fourth aspect of the present invention involves a catheter assemblycapable of insertion into a selected blood vessel in the vascular systemof a patient. The catheter assembly includes an elongated catheter bodyincluding an operative element having an interior at a distal portion ofthe catheter body, an integrated elongated bi-lumen member locatedwithin the catheter body and including a first lumen adapted to receivea guide wire and a second lumen, the second lumen comprising either asupply lumen to deliver a working fluid to the interior of the operativeelement or a return lumen to return a working fluid from the interior ofthe operative element, and a third lumen within the catheter body andcomprising either a supply lumen to deliver a working fluid to aninterior of the operative element or a return lumen to return a workingfluid from the interior of the operative element.

Any of the implementations described above with respect to the thirdaspect of the invention also apply to the fourth aspect of theinvention.

A fifth aspect of the invention involves a method of manufacturing acatheter assembly for heating or cooling a surrounding fluid in a bloodvessel. The method involves extruding an elongated catheter body;locating a heat transfer element including an interior at a distalportion of the catheter body; extruding an integrated elongated bi-lumenmember including a first lumen adapted to receive a guide wire and asecond lumen, the second lumen comprising either a supply lumen todeliver a working fluid to an interior of the heat transfer element or areturn lumen to return a working fluid from the interior of the heattransfer element; and providing the integrated bi-lumen membersubstantially within the elongated catheter body so that a third lumenis formed, the third lumen comprising either a supply lumen to deliver aworking fluid to an interior of the heat transfer element or a returnlumen to return a working fluid from the interior of the heat transferelement.

Implementations of the fifth aspect of the invention may include one ormore of the following. The second lumen has a hydraulic diameter and thethird lumen has a hydraulic diameter, and the ratio of the hydraulicdiameter of the second lumen to the hydraulic diameter of the thirdlumen is substantially equal to 0.75. The step of providing theintegrated bi-lumen member substantially within the elongated catheterbody includes simultaneously extruding the integrated bi-lumen membersubstantially within the elongated catheter body.

A sixth aspect of the present invention involves a method ofmanufacturing a catheter assembly. The method includes extruding anelongated catheter body; locating an operative element including aninterior at a distal portion of the catheter body; extruding anintegrated elongated bi-lumen member including a first lumen adapted toreceive a guide wire and a second lumen, the second lumen comprisingeither a supply lumen to deliver a working fluid to an interior of theoperative element or a return lumen to return a working fluid from theinterior of the operative element; and providing the integrated bi-lumenmember substantially within the elongated catheter body so that a thirdlumen is formed, the third lumen comprising either a supply lumen todeliver a working fluid to an interior of the operative element or areturn lumen to return a working fluid from the interior of theoperative element.

Any of the implementations described above with respect to the fifthaspect of the invention also apply to the sixth aspect of the invention.

A seventh aspect of the present invention involves a device for heatingor cooling a surrounding fluid in a blood vessel. The device includes anelongated catheter body, a heat transfer element located at a distalportion of the catheter body and including an interior distal portionand an interior portion defining at least a first heat transfer segmentand a second heat transfer segment, and at least one elongated supplylumen located within the catheter body, the at least one elongatedsupply lumen including first means for delivering working fluid to theinterior distal portion of the first heat transfer segment and secondmeans for delivering working fluid to the interior portion of the secondheat transfer segment.

In an implementation of the seventh aspect of the invention, the secondworking fluid delivering means is adapted to deliver working fluid tothe interior portion of the heat transfer element near a midpoint of theheat transfer element.

An eighth aspect of the present invention involves a device for heatingor cooling a surrounding fluid in a blood vessel. The device includes anelongated catheter body, a heat transfer element located at a distalportion of the catheter body and including an interior distal portionand an interior portion, and at least one elongated supply lumen locatedwithin the catheter body, the at least one elongated supply lumenincluding first means for delivering working fluid to the interiordistal portion of the heat transfer element and second means fordelivering working fluid to the interior portion of the heat transferelement at one or more points proximal to the distal portion of the heattransfer element.

In an implementation of the eighth aspect of the invention, the secondworking fluid delivering means is adapted to deliver working fluid tothe interior portion of the heat transfer element near a midpoint of theheat transfer element.

A ninth aspect of the present invention involves a device for heating orcooling a surrounding fluid in a blood vessel. The device includes anelongated catheter body, a heat transfer element located at a distalportion of the catheter body and including an interior distal portionand an interior portion defining at least a first heat transfer segmentand a second heat transfer segment, a first elongated supply lumenlocated within the catheter body and terminating at the interior distalportion of the heat transfer element into first means for deliveringworking fluid to the interior distal portion of the heat transferelement, and a second elongated supply lumen located within the catheterbody and terminating at a point proximal to the distal portion of theheat transfer element into second means for delivering working fluid tothe interior portion of the heat transfer element at a point proximal tothe distal portion of the heat transfer element.

In an implementation of the ninth aspect of the invention, the secondworking fluid delivering means is adapted to deliver working fluid tothe interior portion of the heat transfer element near a midpoint of theheat transfer element.

A tenth aspect of the present invention involves a device for heating orcooling a surrounding fluid in a blood vessel. The device includes anelongated catheter body, a heat transfer element located at a distalportion of the catheter body and including an interior distal portionand an interior portion defining at least a first heat transfer segmentinterior portion and a second heat transfer segment interior portion, afirst elongated supply lumen located within the catheter body andterminating at the interior distal portion of the first heat transfersegment into first means for delivering working fluid to the interior ofthe first heat transfer segment, and a second elongated supply lumenlocated within the catheter body and terminating at a point proximal tothe distal portion of the heat transfer element into second means fordelivering working fluid to the interior portion of the second heattransfer segment.

In an implementation of the tenth aspect of the invention, the secondworking fluid delivering means is adapted to deliver working fluid tothe interior portion of the heat transfer element near a midpoint of theheat transfer element.

An eleventh aspect of the present invention involves a device forheating or cooling a surrounding fluid in a blood vessel. The deviceincludes an elongated catheter body, a heat transfer element located ata distal portion of the catheter body and including an interior portionadapted to induce mixing of a working fluid to effect heat transferbetween the heat transfer element and working fluid, the heat transferelement including at least a first heat transfer segment, a second heattransfer segment, and an intermediate segment between the first heattransfer segment and the second heat transfer segment, an elongatedsupply lumen member located within the catheter body and adapted todeliver the working fluid to the interior of the heat transfer element,the supply lumen member including a circular outer surface, an elongatedreturn lumen defined in part by the outer surface of the supply lumenmember and the interior portion of the heat transfer element and adaptedto return the working fluid from the interior of the heat transferelement, and wherein the distance between the interior portion of theheat transfer element and the outer surface of the supply lumen memberadjacent the intermediate segment is less than the distance between theinterior portion of the heat transfer element and the outer surface ofthe supply lumen member adjacent the first heat transfer segment.

Implementations of the eleventh aspect of the invention may include oneor more of the following. The distance between the interior portion ofthe heat transfer element and the outer surface of the supply lumenmember adjacent the intermediate segment is such that the characteristicflow resulting from a flow of working fluid is at least of atransitional nature. The intermediate segment includes an interiordiameter that is less than the interior diameter of the first heattransfer segment or the second heat transfer segment. The supply lumenmember includes an outer diameter adjacent the intermediate segment thatis greater than its outer diameter adjacent the first heat transfersegment or the second heat transfer segment. The supply lumen membercomprises a multiple-lumen member. The supply lumen member includes asupply lumen having a hydraulic diameter and the return lumen has ahydraulic diameter substantially equal to 0.75 the hydraulic diameter ofthe supply lumen. The intermediate segment includes a flexible bellowsjoint.

A twelfth aspect of the present invention involves a device for heatingor cooling a surrounding fluid in a blood vessel. The device includes anelongated catheter body, a heat transfer element located at a distalportion of the catheter body and including an interior portion adaptedto induce mixing of a working fluid to effect heat transfer between theheat transfer element and working fluid, an elongated supply lumenmember located within the catheter body and adapted to deliver theworking fluid to the interior of the heat transfer element, an elongatedreturn lumen member located within the catheter body and adapted toreturn the working fluid from the interior of the heat transfer element,and means located within the heat transfer element for further enhancingmixing of the working fluid to effect further heat transfer between theheat transfer element and working fluid.

Implementations of the twelfth aspect of the invention may include oneor more of the following. The supply lumen member comprises amultiple-lumen member having a circular outer surface. The supply lumenmember includes a supply lumen having a hydraulic diameter and thereturn lumen has a hydraulic diameter substantially equal to 0.75 of thehyrdraulic diameter of the supply lumen.

A thirteenth aspect of the present invention involves a device forheating or cooling a surrounding fluid in a blood vessel. The deviceincludes an elongated catheter body, a heat transfer element located ata distal portion of the catheter body and including an interior portionadapted to induce mixing of a working fluid to effect heat transferbetween the heat transfer element and working fluid, an elongated supplylumen member located within the catheter body and adapted to deliver theworking fluid to the interior of the heat transfer element, an elongatedreturn lumen member located within the catheter body and adapted toreturn the working fluid from the interior of the heat transfer element,and a mixing-enhancing mechanism located within the heat transferelement and adapted to further mix the working fluid to effect furtherheat transfer between the heat transfer element and working fluid.

Implementations of the thirteenth aspect of the invention may includeone or more of the following. The supply lumen member comprises amultiple-lumen member having a circular outer surface. The supply lumenmember includes a supply lumen having a hydraulic diameter and thereturn lumen has a hydraulic diameter substantially equal to thehydraulic diameter of the supply lumen.

A fourteenth aspect of the present invention involves a method ofheating or cooling a surrounding fluid in a blood vessel. The methodincludes providing a device for heating or cooling a surrounding fluidin a blood vessel within the blood stream of a blood vessel, the deviceincluding an elongated catheter body, a heat transfer element located ata distal portion of the catheter body and including an interior portionadapted to induce mixing of a working fluid to effect heat transferbetween the heat transfer element and working fluid, an elongated supplylumen member located within the catheter body and adapted to deliver theworking fluid to the interior of the heat transfer element, an elongatedreturn lumen member located within the catheter body and adapted toreturn the working fluid from the interior of the heat transfer element,and a mixing-enhancing mechanism located within the heat transferelement and adapted to further mix the working fluid to effect furtherheat transfer between the heat transfer element and working fluid;causing a working fluid to flow to and along the interior portion of theheat transfer element of the device using the supply lumen and returnlumen; facilitating the transfer of heat between the working fluid andthe heat transfer element by effecting mixing of the working fluid withthe interior portion adapted to induce mixing of a working fluid;facilitating additional transfer of heat between the working fluid andthe heat transfer element by effecting further mixing of the workingfluid with the interior portion with the mixing-enhancing mechanism;causing heat to be transferred between the blood stream and the heattransfer element by the heat transferred between the heat transferelement and working fluid.

The novel features of this invention, as well as the invention itself,will be best understood from the attached drawings, taken along with thefollowing description, in which similar reference characters refer tosimilar parts, and in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the Nusselt number(Nu) and the Reynolds number (Re) for air flowing through a long heatedpipe at uniform wall temperature.

FIG. 2 is a front view of a first embodiment of a mixing-inducing heattransfer element according to the principles of the invention within anartery;

FIG. 3 is a more detailed front view of the heat transfer element ofFIG. 1;

FIG. 4 is a front sectional view of the heat transfer element of FIG. 1;

FIG. 5 is a transverse sectional view of the heat transfer element ofFIG. 1;

FIG. 6 is a front perspective view of the heat transfer element of FIG.1 in use within a partially broken away blood vessel;

FIG. 7 is a partially broken away front perspective view of a secondembodiment of a mixing-inducing heat transfer element according to theprinciples of the invention;

FIG. 8 is a transverse sectional view of the heat transfer element ofFIG. 7;

FIG. 9 is a schematic representation of the invention being used to coolthe brain of a patient;

FIG. 10 is a front sectional view of a guide catheter according to anembodiment of the invention which may be employed for applications ofthe heat transfer element according to the principles of the invention;

FIG. 11 is a front sectional view of a third embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a return tube/guide catheter;

FIG. 12 is a front sectional view of a fourth embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a delivery catheter;

FIG. 13 is a front sectional view of the fourth embodiment of FIG. 12further employing a working fluid catheter;

FIG. 14 is a front sectional view of a fifth embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a guide wire;

FIG. 15 is a front sectional view of a sixth embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a delivery lumen;

FIG. 16 is a front sectional view of an seventh embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a delivery lumen;

FIG. 17 is a front sectional view of an eighth embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a delivery lumen, this delivery lumennon-coaxial with the central body of the catheter;

FIG. 18 is a front sectional view of a ninth embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing multiple lumens;

FIG. 19 is a cross-sectional view of the ninth embodiment of FIG. 18,taken along lines 19—19 of FIG. 18;

FIG. 20 is a front sectional view of a tenth embodiment of a catheteremploying a heat transfer element according to the principles of theinvention;

FIG. 21 is a front sectional view of a further embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a side-by-side lumen arrangement constructedin accordance with an embodiment of the invention;

FIG. 22 is a cross-sectional view of the catheter of FIG. 21 taken alongline 22—22 of FIG. 21;

FIG. 23 is a front sectional view of a catheter employing a heattransfer element and lumen arrangement constructed in accordance with afurther embodiment of the invention;

FIG. 24 is a front sectional view of a catheter employing a heattransfer element and lumen arrangement constructed in accordance with astill further embodiment of the invention; and

FIG. 25 is a front sectional view of a another embodiment of a catheteremploying a heat transfer element according to the principles of theinvention further employing a side-by-side lumen arrangement constructedin accordance with another embodiment of the invention; and

FIG. 26 is a cross-sectional view of the heat transfer elementillustrated in FIG. 25 taken along line 26—26 of FIG. 25.

DETAILED DESCRIPTION OF THE INVENTION

The temperature of a selected organ may be intravascularly regulated bya heat transfer element placed in the organ's feeding artery to absorbor deliver heat to or from the blood flowing into the organ. While themethod is described with respect to blood flow into an organ, it isunderstood that heat transfer within a volume of tissue is analogous. Inthe latter case, heat transfer is predominantly by conduction.

The heat transfer may cause either a cooling or a heating of theselected organ. A heat transfer element that selectively alters thetemperature of an organ should be capable of providing the necessaryheat transfer rate to produce the desired cooling or heating effectwithin the organ to achieve a desired temperature. If placed in thevenous system, whole body cooling may also be effected.

On the arterial side, the heat transfer element should be small andflexible enough to fit within the feeding artery while still allowing asufficient blood flow to reach the organ in order to avoid ischemicorgan damage. Feeding arteries, like the carotid artery, branch off theaorta at various levels. Subsidiary arteries continue to branch offthese initial branches. For example, the internal carotid arterybranches off the common carotid artery near the angle of the jaw. Theheat transfer element is typically inserted into a peripheral artery,such as the femoral artery, using a guide catheter or guide wire, andaccesses a feeding artery by initially passing though a series of one ormore of these branches. Thus, the flexibility and size, e.g., thediameter, of the heat transfer element are important characteristics.This flexibility is achieved as is described in more detail below.

These points are illustrated using brain cooling as an example. Otherorgans, as well as the whole body, may also be cooled. The commoncarotid artery supplies blood to the head and brain. The internalcarotid artery branches off the common carotid artery to supply blood tothe anterior cerebrum. The heat transfer element may be placed into thecommon carotid artery or into both the common carotid artery and theinternal carotid artery.

The benefits of hypothermia described above are achieved when thetemperature of the blood flowing to the brain is reduced to between 30°C. and 32° C. A typical brain has a blood flow rate through each carotidartery (right and left) of approximately 250-375 cubic centimeters perminute (cc/min). With this flow rate, calculations show that the heattransfer element should absorb approximately 75-175 watts of heat whenplaced in one of the carotid arteries to induce the desired coolingeffect. Smaller organs may have less blood flow in their respectivesupply arteries and may require less heat transfer, such as about 25watts.

The method employs conductive and convective heat transfers. Once thematerials for the device and a working fluid are chosen, the conductiveheat transfers are solely dependent on the temperature gradients.Convective heat transfers, by contrast, also rely on the movement offluid to transfer heat. Forced convection results when the heat transfersurface is in contact with a fluid whose motion is induced (or forced)by a pressure gradient, area variation, or other such cause. In the caseof arterial flow, the beating heart provides an oscillatory pressuregradient to force the motion of the blood in contact with the heattransfer surface. One of the aspects of the device uses turbulence toenhance this forced convective heat transfer.

The rate of convective heat transfer Q is proportional to the product ofS, the area of the heat transfer element in direct contact with thefluid, ΔT=T_(b)−T_(s), the temperature differential between the surfacetemperature T_(s) of the heat transfer element and the free stream bloodtemperature T_(b), and {overscore (h_(c)+L )}, the average convectionheat transfer coefficient over the heat transfer area. {overscore(h_(c)+L )} is sometimes called the “surface coefficient of heattransfer” or the “convection heat transfer coefficient”.

The magnitude of the heat transfer rate Q to or from the fluid flow canbe increased through manipulation of the above three parameters.Practical constraints limit the value of these parameters and how muchthey can be manipulated. For example, the internal diameter of thecommon carotid artery ranges from 6 to 8 mm. Thus, the heat transferelement residing therein may not be much larger than 4 mm in diameter toavoid occluding the vessel. The length of the heat transfer elementshould also be limited. For placement within the internal and commoncarotid artery, the length of the heat transfer element is limited toabout 10 cm. This estimate is based on the length of the common carotidartery, which ranges from 8 to 12 cm.

Consequently, the value of the surface area S is limited by the physicalconstraints imposed by the size of the artery into which the device isplaced. Surface features can be used to increase the surface area of theheat transfer element; however, these features alone generally cannotprovide enough surface area enhancement to meet the required heattransfer rate to effectively cool the brain.

One may also attempt to vary the magnitude of the heat transfer rate byvarying ΔT. The value of ΔT=T_(b)−T_(s) can be varied by varying thesurface temperature T_(s) of the heat transfer element. The allowablesurface temperature of the heat transfer element is limited by thecharacteristics of blood. The blood temperature is fixed at about 37°C., and blood freezes at approximately 0° C. When the blood approachesfreezing, ice emboli may form in the blood which may lodge downstream,causing serious ischemic injury. Furthermore, reducing the temperatureof the blood also increases its viscosity which results in a smalldecrease in the value of {overscore (h_(c)+L )}. Increased viscosity ofthe blood may furher result in an increase in the pressure drop withinthe artery, thus compromising the flow of blood to the brain. Given theabove constraints, it is advantageous to limit the surface temperatureof the heat transfer element to approximately 1° C.-5° C., thusresulting in a maximum temperature differential between the blood streamand the heat transfer element of approximately 32° C.-36° C.

One may also attempt to vary the magnitude of the heat transfer rate byvarying {overscore (h_(c)+L )}. Fewer constraints are imposed on thevalue of the convection heat transfer coefficient {overscore (h_(c)+L)}. The mechanisms by which the value of {overscore (h_(c)+L )} may beincreased are complex. However, one way to increase {overscore (h_(c)+L)} for a fixed mean value of the velocity is to increase the level ofturbulent kinetic energy in the fluid flow.

The heat transfer rate Q_(no-flow) in the absence of fluid flow isproportional to ΔT, the temperature differential between the surfacetemperature T_(s) of the heat transfer element and the free stream bloodtemperature T_(b) times k, the diffusion constant, and is inverselyproportion to distance D across which heat is being transferred.

The magnitude of the enhancement in heat transfer by fluid flow can beestimated by taking the ratio of the heat transfer rate with fluid flowto the heat transfer rate in the absence of fluid flowN=Q_(flow)/Q_(no-flow)={overscore (h_(c)+L )}/(k/δ). This ratio iscalled the Nusselt number (“Nu”). For convective heat transfer betweenblood and the surface of the heat transfer element, Nusselt numbers of50-80 have been found to be appropriate for selective coolingapplications of various organs in the human body. Nusselt numbers aregenerally dependent on several other numbers: the Reynolds number, theWomersley number, and the Prandtl number.

For example, FIG. 1 illustrates the dependency of the Nusselt number onthe Reynolds number for a fluid flowing through a long duct, i.e., airflowing though a long heated pipe at a uniform wall temperature.Although FIG. 1 illustrates this relationship for a different fluidthrough a different structure, the inventors of the present inventionbelieve a similar relationship exists for blood flow through a bloodvessel. FIG. 1 illustrates that flow is laminar when the Reynolds numberis below some number, in this case about 2100. In the range of Reynoldsnumbers between another set of numbers, in this case 2100 and 10,000, atransition from laminar to turbulent flow takes place. The flow in thisregime is called transitional. The mixing caused by the heat transferelement of the present invention produces a flow that is at leasttransitional. At another Reynolds number, in the case above, about10,000, the flow becomes fully turbulent.

The type of flow that occurs is important because in laminar flowthrough a duct, there is no mixing of warmer and colder fluid particlesby eddy motion. Thus, the only heat transfer that takes place is throughconduction. Since most fluids have small thermal conductivities, theheat transfer coefficients in laminar flow are relatively small. Intransitional and turbulent flow, mixing occurs through eddies that carrywarmer fluid into cooler regions and vice versa. Since the mixingmotion, even if it is only on a small scale compared to fully turbulentflow, accelerates the transfer of heat considerably, a marked increasein the heat transfer coefficient occurs above a certain Reynolds number,which in the graph of FIG. 1 is about 2100. It can be seen from FIG. 1that it is at approximately this point where the Nusselt numberincreases more dramatically. A different set of numbers may be measuredfor blood flow through an artery or vein. However, the inventors believethat a Nusselt number at least in the transitional region is importantfor enhanced heat transfer.

Stirring-type mechanisms, which abruptly change the direction ofvelocity vectors, may be utilized to induce at least transitional flow,increasing the heat transfer rate by this eddy creation. The level ofturbulence or mixing so created is characterized by the turbulenceintensity . Turbulence intensity is defined as the root mean square ofthe fluctuating velocity divided by the mean velocity. Such mechanismscan create high levels of turbulence intensity in the free stream,thereby increasing the heat transfer rate. This turbulence intensityshould ideally be sustained for a significant portion of the cardiaccycle, and should ideally be created throughout the free stream and notjust in the boundary layer.

Turbulence does occur for a short period in the cardiac cycle anyway. Inparticular, the blood flow is turbulent during a small portion of thedescending systolic flow. This portion is less than 20% of the period ofthe cardiac cycle. If a heat transfer element is placed co-axiallyinside an artery, the heat transfer rate will be enhanced during thisshort interval. For typical of these fluctuations, the turbulenceintensity is at least 0.05. In other words, the instantaneous velocityfluctuations deviate from the mean velocity by at least 5%. In someembodiments, lower fluctuations may be employed, such as 3% or even 2%.Although ideally turbulence is created throughout the entire period ofthe cardiac cycle, the benefits of turbulence are obtained if theturbulence or mixing is sustained for 75%, 50% or even as low as 30% or20% of the cardiac cycle. Of course, such turbulence or mixing is muchless, or is even non-existent, in veins or in very small arteries.

One type of mixing-inducing heat transfer element which may beadvantageously employed is a heat transfer element made of a highthermal conductivity material, such as metal. The use of a high thermalconductivity material increases the heat transfer rate for a giventemperature differential between the coolant within the heat transferelement and the blood. This facilitates the use of a higher temperaturecoolant within the heat transfer element, allowing safer coolants, suchas water, to be used. Highly thermally conductive materials, such asmetals, tend to be rigid. Bellows provided a high degree of articulationthat compensated for the intrinsic stiffness of the metal. In anotherembodiment, the bellows may be replaced with a straight metal tubehaving a predetermined thickness to allow flexibility via bending of themetal. Alternatively, the bellows may be replaced with a polymer tube,e.g., a latex rubber tube, a plastic tube, or a flexible plasticcorrugated tube.

The device size may be minimized, e.g., less than 4 mm, to preventblockage of the blood flowing in the vessel. The design of the heattransfer element should facilitate flexibility in an inherentlyinflexible material.

To create the desired level of turbulence intensity in the blood freestream during the whole cardiac cycle, one embodiment of the device usesa modular design. This design creates helical blood flow and produces ahigh level of mixing in the free stream by periodically forcing abruptchanges in the direction of the helical blood flow. FIG. 2 is aperspective view of such a mixing-inducing heat transfer element withinan artery. Transitional to turbulent flow would be found at point 114,in the free stream area. The abrupt changes in flow direction areachieved through the use of a series of two or more heat transfersegments, each comprised of one or more helical ridges.

The use of periodic abrupt changes in the helical direction of the bloodflow in order to induce strong free stream turbulence or mixing may beillustrated with reference to a common clothes washing machine. Therotor of a washing machine spins initially in one direction causinglaminar flow. When the rotor abruptly reverses direction, significantmixing is created within the entire wash basin as the changing currentscause random turbulent motion within the clothes-water slurry.

FIG. 3 is an elevation view of one embodiment of a heat transfer element14. The heat transfer element 14 is comprised of a series of elongated,articulated segments or modules 20, 22, 24. Three such segments areshown in this embodiment, but one or more such segments could be used.As seen in FIG. 3, a first elongated heat transfer segment 20 is locatedat the proximal end of the heat transfer element 14. A mixing inducingexterior surface of the segment 20 comprises four parallel helicalridges 28 with four parallel helical grooves 26 therebetween. One, two,three, or more parallel helical ridges 28 could also be used. In thisembodiment, the helical ridges 28 and the helical grooves 26 of the heattransfer segment 20 have a left hand twist, referred to herein as acounter-clockwise spiral or helical rotation, as they proceed toward thedistal end of the heat transfer segment 20.

The first heat transfer segment 20 is coupled to a second elongated heattransfer segment 22 by a first tube section 25, which providesflexibility. The second heat transfer segment 22 comprises one or morehelical ridges 32 with one or more helical grooves 30 therebetween. Theridges 32 and grooves 30 have a right hand, or clockwise, twist as theyproceed toward the distal end of the heat transfer segment 22. Thesecond heat transfer segment 22 is coupled to a third elongated heattransfer segment 24 by a second tube section 27. The third heat transfersegment 24 comprises one or more helical ridges 36 with one or morehelical grooves 34 therebetween. The helical ridge 36 and the helicalgroove 34 have a left hand, or counter-clockwise, twist as they proceedtoward the distal end of the heat transfer segment 24. Thus, successiveheat transfer segments 20, 22, 24 of the heat transfer element 14alternate between having clockwise and counterclockwise helical twists.The actual left or right hand twist of any particular segment isimmaterial, as long as adjacent segments have opposite helical twist.

In addition, the rounded contours of the ridges 28, 32, 36 also allowthe heat transfer element 14 to maintain a relatively a traumaticprofile, thereby minimizing the possibility of damage to the bloodvessel wall. A heat transfer element may be comprised of one, two,three, or more heat transfer segments.

The tube sections 25, 27 are formed from seamless and nonporousmaterials, such as metal, and therefore are impermeable to gas, whichcan be particularly important, depending on the type of working fluidthat is cycled through the heat transfer element 14. The structure ofthe tube sections 25, 27 allows them to bend, extend and compress, whichincreases the flexibility of the heat transfer element 14 so that it ismore readily able to navigate through blood vessels. The tube sections25, 27 are also able to tolerate cryogenic temperatures without a lossof performance. The tube sections 25, 27 may have a predeterminedthickness of their walls, such as between about 0.5 and 0.8 mils. Thepredetermined thickness is to a certain extent dependent on the diameterof the overall tube. Thicknesses of 0.5 to 0.8 mils may be appropriateespecially for a tubal diameter of about 4 mm. For smaller diameters,such as about 3.3 mm, larger thicknesses may be employed for higherstrength. In another embodiment, tube sections 25, 27 may be formed froma polymer material such as rubber, e.g., latex rubber.

The exterior surfaces of the heat transfer element 14 can be made frommetal except in flexible joint embodiments where the surface may becomprised of a polymer material. The metal may be a very high thermalconductivity material such as nickel, thereby facilitating efficientheat transfer. Alternatively, other metals such as stainless steel,titanium, aluminum, silver, copper and the like, can be used, with orwithout an appropriate coating or treatment to enhance biocompatibilityor inhibit clot formation. Suitable biocompatible coatings include,e.g., gold, platinum or polymer paralyene. The heat transfer element 14may be manufactured by plating a thin layer of metal on a mandrel thathas the appropriate pattern. In this way, the heat transfer element 14may be manufactured inexpensively in large quantities, which is animportant feature in a disposable medical device.

Because the heat transfer element 14 may dwell within the blood vesselfor extended periods of time, such as 24-48 hours or even longer, it maybe desirable to treat the surfaces of the heat transfer element 14 toavoid clot formation. One means by which to prevent thrombus formationis to bind an antithrombogenic agent to the surface of the heat transferelement 14. For example, heparin is known to inhibit clot formation andis also known to be useful as a biocoating. Alternatively, the surfacesof the heat transfer element 14 may be bombarded with ions such asnitrogen. Bombardment with nitrogen can harden and smooth the surfaceand thus prevent adherence of clotting factors to the surface.

FIG. 4 is a longitudinal sectional view of the heat transfer element 14,taken along line 4—4 in FIG. 3. Some interior contours are omitted forpurposes of clarity. An inner tube 42 creates an inner coaxial lumen 40and an outer coaxial lumen 46 within the heat transfer element 14. Oncethe heat transfer element 14 is in place in the blood vessel, a workingfluid such as saline or other aqueous solution may be circulated throughthe heat transfer element 14. Fluid flows up a supply catheter into theinner coaxial lumen 40. At the distal end of the heat transfer element14, the working fluid exits the inner coaxial lumen 40 and enters theouter lumen 46. As the working fluid flows through the outer lumen 46,heat is transferred between the working fluid and the exterior surface37 of the heat transfer element 14. Because the heat transfer element 14is constructed from a high conductivity material, the temperature of itsexterior surface 37 may approach the temperature of the working fluid.The tube 42 may be formed as an insulating divider to thermally separatethe inner lumen 40 from the outer lumen 46. For example, insulation maybe achieved by creating longitudinal air channels in the wall of theinsulating tube 42. Alternatively, the insulating tube 42 may beconstructed of a non-thermally conductive material likepolytetrafluoroethylene or some other polymer.

It is important to note that the same mechanisms that govern the heattransfer rate between the exterior surface 37 of the heat transferelement 14 and the blood also govern the heat transfer rate between theworking fluid and the interior surface 38 of the heat transfer element14. The heat transfer characteristics of the interior surface 38 areparticularly important when using water, saline or other fluid whichremains a liquid as the coolant. Other coolants such as freon undergonucleate boiling and create turbulence through a different mechanism.Saline is a safe coolant because it is non-toxic, and leakage of salinedoes not result in a gas embolism, which could occur with the use ofboiling refrigerants. Since turbulence or mixing in the coolant isenhanced by the shape of the interior surface 38 of the heat transferelement 14, the coolant can be delivered to the heat transfer element 14at a warmer temperature and still achieve the necessary heat transferrate.

This has a number of beneficial implications in the need for insulationalong the catheter shaft length. Due to the decreased need forinsulation, the catheter shaft diameter can be made smaller. Theenhanced heat transfer characteristics of the interior surface of theheat transfer element 14 also allow the working fluid to be delivered tothe heat transfer element 14 at lower flow rates and lower pressures.High pressures may make the heat transfer element stiff and cause it topush against the wall of the blood vessel, thereby shielding part of theexterior surface 37 of the heat transfer element 14 from the blood.Because of the increased heat transfer characteristics achieved by thealternating helical ridges 28, 32, 36, the pressure of the working fluidmay be as low as 5 atmospheres, 3 atmospheres, 2 atmospheres or evenless than 1 atmosphere.

FIG. 5 is a transverse sectional view of the heat transfer element 14,taken at a location denoted by the line 5—5 in FIG. 3. FIG. 5illustrates a five-lobed embodiment, whereas FIG. 3 illustrates afour-lobed embodiment. As mentioned earlier, any number of lobes mightbe used. In FIG. 5, the coaxial construction of the heat transferelement 14 is clearly shown. The inner coaxial lumen 40 is defined bythe insulating coaxial tube 42. The outer lumen 46 is defined by theexterior surface of the insulating coaxial tube 42 and the interiorsurface 38 of the heat transfer element 14. In addition, the helicalridges 32 and helical grooves 30 may be seen in FIG. 5. In the preferredembodiment, the depth of the grooves, d_(i), may be greater than theboundary layer thickness which would have developed if a cylindricalheat transfer element were introduced. For example, in a heat transferelement 14 with a 4 mm outer diameter, the depth of the invaginations,d_(i), may be approximately equal to 1 mm if designed for use in thecarotid artery. Although FIG. 5 shows four ridges and four grooves, thenumber of ridges and grooves may vary. Thus, heat transfer elements with1, 2, 3, 4, 5, 6, 7, 8 or more ridges are specifically contemplated.

FIG. 6 is a perspective view of a heat transfer element 14 in use withina blood vessel, showing only one helical lobe per segment for purposesof clarity. Beginning from the proximal end of the heat transfer element(not shown in FIG. 6), as the blood moves forward during the systolicpulse, the first helical heat transfer segment 20 induces acounter-clockwise rotational inertia to the blood. As the blood reachesthe second segment 22, an unstable shear layer is produced that causesmixing within the blood. Further, as the blood reaches the third segment24, the rotational direction of the inertia is again reversed. Thesudden changes in flow direction actively reorient and randomize thevelocity vectors, thus ensuring mixing throughout the bloodstream.During transitional to turbulent flow, the velocity vectors of the bloodbecome more random and, in some cases, become perpendicular to the axisof the artery. In addition, as the velocity of the blood within theartery decreases and reverses direction during the cardiac cycle,additional mixing is induced and sustained throughout the duration ofeach pulse through the same mechanisms described above.

Thus, a large portion of the volume of warm blood in the vessel isactively brought in contact with the heat transfer element 14, where itcan be cooled by direct contact rather than being cooled largely byconduction through adjacent laminar layers of blood. As noted above, thedepth of the grooves 26, 30, 34 (FIG. 3) is greater than the depth ofthe boundary layer that would develop if a straight-walled heat transferelement were introduced into the blood stream. In this way, mixing isinduced. In the preferred embodiment, in order to create the desiredlevel of mixing in the entire blood stream during the whole cardiaccycle, the heat transfer element 14 creates a turbulence intensitygreater than about 0.05. The turbulence intensity may be greater than0.05, 0.06, 0.07 or up to 0.8 or 0.20 or greater.

Referring back to FIG. 3, the heat transfer element 14 has been designedto address all of the design criteria discussed above. First, the heattransfer element 14 is flexible and is made of a highly conductivematerial. The flexibility is provided by a segmental distribution oftube sections 25, 27 which provide an articulating mechanism. The tubesections have a predetermined thickness which provides sufficientflexibility. Second, the exterior surface area 37 has been increasedthrough the use of helical ridges 28, 32, 36 and helical grooves 26, 30,34. The ridges also allow the heat transfer element 14 to maintain arelatively a traumatic profile, thereby minimizing the possibility ofdamage to the vessel wall. Third, the heat transfer element 14 has beendesigned to promote mixing both internally and externally. The modularor segmental design allows the direction of the invaginations to bereversed between segments. The alternating helical rotations create analternating flow that results in a mixing of the blood in a manneranalogous to the mixing action created by the rotor of a washing machinethat switches directions back and forth. This mixing action is intendedto promote a high level of mixing or turbulent kinetic energy to enhancethe heat transfer rate. The alternating helical design also causesbeneficial mixing, or turbulent kinetic energy, of the working fluidflowing internally.

FIG. 7 is a cut-away perspective view of an alternative embodiment of aheat transfer element 50. An external surface 52 of the heat transferelement 50 is covered with a series of axially staggered protrusions 54.The staggered nature of the outer protrusions 54 is readily seen withreference to FIG. 8 which is a transverse cross-sectional view taken ata location denoted by the line 8—8 in FIG. 7. In order to induce freestream turbulence, the height, d_(p), of the staggered outer protrusions54 is greater than the thickness of the boundary layer which woulddevelop if a smooth heat transfer element had been introduced into theblood stream. As the blood flows along the external surface 52, itcollides with one of the staggered protrusions 54 and a turbulent wakeflow is created behind the protrusion. As the blood divides and swirlsalong side of the first staggered protrusion 54, its turbulent wakeencounters another staggered protrusion 54 within its path preventingthe re-lamination of the flow and creating yet more mixing. In this way,the velocity vectors are randomized and mixing is created not only inthe boundary layer but also throughout the free stream. As is the casewith the preferred embodiment, this geometry also induces a mixingeffect on the internal coolant flow.

A working fluid is circulated up through an inner coaxial lumen 56defined by an insulating coaxial tube 58 to a distal tip of the heattransfer element 50. The working fluid then traverses an outer coaxiallumen 60 in order to transfer heat to the exterior surface 52 of theheat transfer element 50. The inside surface of the heat transferelement 50 is similar to the exterior surface 52, in order to inducemixing flow of the working fluid. The inner protrusions can be alignedwith the outer protrusions 54, as shown in FIG. 8, or they can be offsetfrom the outer protrusions 54, as shown in FIG. 7.

FIG. 9 is a schematic representation of an embodiment of the inventionbeing used to cool the brain of a patient. A selective organ hypothermiaapparatus shown in FIG. 9 includes a working fluid supply 10, preferablysupplying a chilled liquid such as water, alcohol or a halogenatedhydrocarbon, a supply catheter 12 and the heat transfer element 14. Thesupply catheter 12 has a coaxial construction. An inner coaxial lumenwithin the supply catheter 12 receives coolant from the working fluidsupply 10. The coolant travels the length of the supply catheter 12 tothe heat transfer element 14 which serves as the cooling tip of thecatheter. At the distal end of the heat transfer element 14, the coolantexits the insulated interior lumen and traverses the length of the heattransfer element 14 in order to decrease the temperature of the heattransfer element 14. The coolant then traverses an outer lumen of thesupply catheter 12 so that it may be disposed of or recirculated. Thesupply catheter 12 is a flexible catheter having a diameter sufficientlysmall to allow its distal end to be inserted percutaneously into anaccessible artery such as the femoral artery of a patient as shown inFIG. 9. The supply catheter 12 is sufficiently long to allow the heattransfer element 14 at the distal end of the supply catheter 12 to bepassed through the vascular system of the patient and placed in theinternal carotid artery or other small artery. The method of insertingthe catheter into the patient and routing the heat transfer element 14into a selected artery is well known in the art. A mentioned above, thedevice may also be placed in the venous system to cause total bodycooling. The device's helices, which are one way of increasing thesurface area as well as to induce mixing or turbulence, enhance heattransfer.

Although the working fluid supply 10 is shown as an exemplary coolingdevice, other devices and working fluids may be used. For example, inorder to provide cooling, freon, perflourocarbon, water, or saline maybe used, as well as other such coolants.

The heat transfer element can absorb or provide over 75 Watts of heat tothe blood stream and may absorb or provide as much as 100 Watts, 150Watts, 170 Watts or more. For example, a heat transfer element with adiameter of 4 mm and a length of approximately 10 cm using ordinarysaline solution chilled so that the surface temperature of the heattransfer element is approximately 5° C. and pressurized at 2 atmospherescan absorb about 100 Watts of energy from the bloodstream. Smallergeometry heat transfer elements may be developed for use with smallerorgans which provide 60 Watts, 50 Watts, 25 Watts or less of heattransfer. For venous cooling, as much as or more than 250 Watts may beextracted.

An exemplary practice of the present invention, for arterialapplications, is illustrated in the following non-limiting example.

Exemplary Procedure

1. The patient is initially assessed, resuscitated, and stabilized.

2. The procedure is carried out in an angiography suite or surgicalsuite equipped with fluoroscopy.

3. Because the catheter is placed into the common carotid artery, it isimportant to determine the presence of stenotic atheromatous lesions. Acarotid duplex (Doppler/ultrasound) scan can quickly and non-invasivelymake this determination. The ideal location for placement of thecatheter is in the left carotid so this may be scanned first. If diseaseis present, then the right carotid artery can be assessed. This test canbe used to detect the presence of proximal common carotid lesions byobserving the slope of the systolic upstroke and the shape of thepulsation. Although these lesions are rare, they could inhibit theplacement of the catheter. Examination of the peak blood flow velocitiesin the internal carotid can determine the presence of internal carotidartery lesions. Although the catheter is placed proximally to suchlesions, the catheter may exacerbate the compromised blood flow createdby these lesions. Peak systolic velocities greater that 130 cm/sec andpeak diastolic velocities>100 cm/sec in the internal indicate thepresence of at least 70% stenosis. Stenosis of 70% or more may warrantthe placement of a stent to open up the internal artery diameter.

4. The ultrasound can also be used to determine the vessel diameter andthe blood flow and the catheter with the appropriately sized heattransfer element are selected.

5. After assessment of the arteries, the patient's inguinal region issterilely prepped and infiltrated with lidocaine.

6. The femoral artery is cannulated and a guide wire may be inserted tothe desired carotid artery. Placement of the guide wire is confirmedwith fluoroscopy.

7. An angiographic catheter can be fed over the wire and contrast mediainjected into the artery to further to assess the anatomy of thecarotid.

8. Alternatively, the femoral artery is cannulated and a 10-12.5 french(f) introducer sheath is placed.

9. A guide catheter is placed into the desired common carotid artery. Ifa guiding catheter is placed, it can be used to deliver contrast mediadirectly to further assess carotid anatomy.

10. A 10 f-12 f (3.3-4.0 mm) (approximate) cooling catheter issubsequently filled with saline and all air bubbles are removed.

11. The cooling catheter is placed into the carotid artery via theguiding catheter or over the guidewire. Placement is confirmed withfluoroscopy.

12. The cooling catheter is connected to a refrigerated pump circuitalso filled with saline and free from air bubbles.

13. Cooling is initiated by starting the refrigerated pump circuit. Thesaline within the cooling catheter is circulated at 3-8 cc/sec. Thesaline travels through the refrigerated pump circuit and is cooled toapproximately 1° C.

14. The saline subsequently enters the cooling catheter where it isdelivered to the heat transfer element. The saline is warmed toapproximately 5-7° C. as it travels along the inner lumen of thecatheter shaft to the end of the heat transfer element.

15. The saline then flows back through the heat transfer element incontact with the inner metallic surface. The saline is further warmed inthe heat transfer element to 12-15° C., and in the process, heat isabsorbed from the blood, cooling the blood to 30° C. to 32° C.

16. The chilled blood then goes on to chill the brain. It is estimatedthat 15-30 minutes will be required to cool the brain to 30 to 32° C.

17. The warmed saline travels back down the outer lumen of the cathetershaft and back to the chilled water bath where it is cooled to 1° C.

18. The pressure drops along the length of the circuit are estimated tobe, e.g., 6 atmospheres.

19. The cooling can be adjusted by increasing or decreasing the flowrate of the saline, or by changing the temperature of the saline.Monitoring of the temperature drop of the saline along the heat transferelement will allow the flow to be adjusted to maintain the desiredcooling effect.

20. The catheter is left in place to provide cooling for up to or morethan 12 to 24 hours.

21. If desired, warm saline can be circulated to promote warming of thebrain at the end of the procedure.

The invention may also be used in combination with other techniques. Forexample, one technique employed to place working lumens or catheters indesired locations employs guide catheters, as mentioned above. Referringto FIG. 10, a guide catheter 102 is shown which may be advantageouslyemployed in the invention. The guide catheter 102 has a soft tapered tip104 and a retaining flange 124 at a distal end 101. The soft tapered tip104 allows an a traumatic entrance of the guide catheter 102 into anartery as well as a sealing function as is described in more detailbelow. The retaining flange 124 may be a metallic member adhered to theguide catheter interior wall or may be integral with the material of thetube. The retaining flange 124 further has a sealing function describedin more detail below.

The guide catheter 102 may have various shapes to facilitate placementinto particular arteries. In the case of the carotid artery, the guidecatheter 102 may have the shape of a hockey stick. The guide catheter102 may include a Pebax® tube with a Teflon® liner. The Teflon® linerprovides sufficient lubricity to allow minimum friction when componentsare pushed through the tube. A metal wire braid may also be employedbetween the Pebax® tube and the Teflon® liner to provide torqueabilityof the guide catheter 102.

A number of procedures may be performed with the guide catheter 102 inplace within an artery or vein. For example, a stent may be disposedacross a stenotic lesion in the internal carotid artery. This procedureinvolves placing a guide wire through the guide catheter 102 and acrossthe lesion. A balloon catheter loaded with a stent is then advancedalong the guide wire. The stent is positioned across the lesion. Theballoon is expanded with contrast, and the stent is deployedintravascularly to open up the stenotic lesion. The balloon catheter andthe guide wire may then be removed from the guide catheter.

A variety of treatments may pass through the guide catheter. Forexample, the guide catheter, or an appropriate lumen disposed within,may be employed to transfer contrast for diagnosis of bleeding orarterial blockage, such as for angiography. The same may further beemployed to deliver various drug therapies, e.g., to the brain. Suchtherapies may include delivery of thrombolytic drugs that lyse clotslodged in the arteries of the brain.

A proximal end 103 of the guide catheter 102 has a male luer connectorfor mating with a y-connector 118 attached to a supply tube 108. Thesupply tube 108 may include a braided Pebax® tube or a polyimide tube.The y-connector 118 connects to the guide catheter 102 via a male/femaleluer connector assembly 116. The y-connector 118 allows the supply tube108 to enter the assembly and to pass through the male/female luerconnector assembly 116 into the interior of the guide catheter 102. Thesupply tube 108 may be disposed with an outlet at its distal end. Theoutlet of the supply tube 108 may also be used to provide a workingfluid to the interior of a heat transfer element 110. The guide catheter102 may be employed as the return tube for the working fluid supply inthis aspect of the invention. In this embodiment, a heat transferelement 110 is delivered to the distal end 101 of the guide catheter 102as is shown in FIG. 11.

In FIG. 11, the heat transfer element 110 is shown, nearly in a workinglocation, in combination with the return tube/guide catheter 102. Inparticular, the heat transfer element 110 is shown near the distal end101 of the return tube/guide catheter (“RTGC”) 102. The heat transferelement 110 may be kept in place by a flange 106 on the heat transferelement 110 that abuts the retaining flange 124 on the RTGC 102. Flanges124 and 106 may also employ o-rings such as an o-ring 107 shown adjacentto the flange 106. Other such sealing mechanisms or designs may also beused. In this way, the working fluid is prevented from leaking into theblood.

The supply tube 108 may connect to the heat transfer element 110 (theconnection is not shown) and may be employed to push the heat transferelement 110 through the guide catheter 102. The supply tube should havesufficient rigidity to accomplish this function. In an alternativeembodiment, a guide wire may be employed having sufficient rigidity topush both the supply tube 108 and the heat transfer element 110 throughthe guide catheter 102. So that the supply tube 108 is preventing fromabutting its outlet against the interior of the heat transfer element110 and thereby stopping the flow of working fluid, a strut 112 may beemployed on a distal end of the supply tube 108. The strut 112 may havea window providing an alternative path for the flowing working fluid.

The heat transfer element 110 may employ any of the forms disclosedabove, as well as variations of those forms. For example, the heattransfer element 110 may employ alternating helical ridges separated byflexible joints, the ridges creating sufficient mixing to enhance heattransfer between a working fluid and blood in the artery. Alternatively,the heat transfer element 110 may be inflatable and may have sufficientsurface area such that the heat transfer due to conduction alone issufficient to provide the requisite heat transfer. Details of the heattransfer element 110 are omitted in FIG. 11 for clarity.

FIG. 12 shows an alternate embodiment of the invention in which a heattransfer element 204 employs an internal supply catheter 216. The heattransfer element 204 is shown with mixing-inducing invaginations 218located thereon. Similar invaginations may be located in the interior ofthe heat transfer element 204 but are not shown for clarity. Further, itshould be noted that the heat transfer element 204 is shown with merelyfour invaginations. Other embodiments may employ multiple elementsconnected by flexible joints as is disclosed above. A single heattransfer element is shown in FIG. 12 merely for clarity.

A return supply catheter 202 is shown coupled to the heat transferelement 204. The return supply catheter may be coupled to the heattransfer element 204 in known fashion, and may provide a convenientreturn path for working fluid as may be provided to the heat transferelement 204 to provide temperature control of a flow or volume of blood.

A delivery catheter 216 is also shown in FIG. 12. The delivery catheter216 may be coupled to a y-connector at its proximal end in the mannerdisclosed above. The delivery catheter 216 may be freely disposed withinthe interior of the return supply catheter 202 except where it isrestrained from further longitudinal movement (in one direction) by aretaining flange 210 disposed at the distal end 208 of the heat transferelement 204. The delivery catheter 216 may be made sufficiently flexibleto secure itself within retaining flange 210, at least for a shortduration. The delivery catheter 216 may have a delivery outlet 212 at adistal end to allow delivery of a drug or other such material fortherapeutic purposes. For example, a radioopaque fluid may be dispensedfor angiography or a thrombolytic drug for thrombolytic applications.

For applications in which it is desired to provide drainage of theartery, e.g., laser ablation, the delivery catheter may be pulledupstream of the retaining flange 210, exposing an annular hole in fluidcommunication with the return supply catheter 202. The return supplycatheter 202 may then be used to drain the volume adjacent the retainingflange 210.

The assembly may also perform temperature control of blood in the arterywhere the same is located. Such temperature control procedures may beperformed, e.g., before or after procedures involving the deliverycatheter 216. Such a device for temperature control is shown in FIG. 13.In this figure, a working fluid catheter 222 is disposed within thereturn supply catheter 202 and the heat transfer element 204. In amanner similar to the delivery catheter 216, the working fluid cathetermay be freely disposed within the interior of the return supply catheter202 and may further be coupled to a y-connector at its proximal end inthe manner disclosed above. The working fluid catheter 222 may furtherbe made sufficiently flexible to secure itself within retaining flange210, at least for a short duration. The working fluid catheter 222 mayhave a plurality of outlets 214 to allow delivery of a working fluid.The outlets 214 are located near the distal end 224 of the working fluidcatheter 222 but somewhat upstream. In this way, the outlets 214 allowdispensation of a working fluid into the interior of the heat transferelement 204 rather than into the blood stream. The working fluidcatheter 222 may also be insulated to allow the working fluid tomaintain a desired temperature without undue heat losses to the walls ofthe working fluid catheter 222.

One method of disposing a heat transfer device within a desired artery,such as the carotid artery, involves use of a guide wire. Referring toFIG. 14, a guide wire 232 is shown disposed within the interior of theheat transfer element 204. The heat transfer element 204 mayconveniently use the hole defined by retaining flange 210 to be threadedonto the guide wire 232.

Numerous other therapies may then employ the return supply catheter andheat transfer element as a “guide catheter”. For example, various laserand ultrasound ablation catheters may be disposed within, as well asmicrocatheters. In this way, these therapeutic techniques may beemployed at nearly the same time as therapeutic temperature control,including, e.g., neuroprotective cooling.

The use of an additional lumen was disclosed above in connection withpassing a variety of treatments through the guide catheter. For example,an additional lumen may be employed to transfer contrast for diagnosisof bleeding or arterial blockage, such as for angiography. Such anadditional lumen may be defined by a drug delivery catheter which formsa part of the overall catheter assembly. The same may be employed todeliver various drug therapies, e.g., to the brain. The use of anadditional lumen was further mentioned in connection with expansion of aballoon that may be used to occlude a drug delivery lumen outlet.

FIG. 15 depicts an implementation of an embodiment of the inventionemploying just such a third lumen. In FIG. 15, a third lumen 316 is asmall central lumen defined by a drag delivery catheter substantiallyparallel to the supply and return catheters. A return catheter 302defining an outlet lumen 320 is coupled to a heat transfer element 304as before. The heat transfer element 304 may have mixing orturbulence-inducing invaginations 306 thereon. Within the heat transferelement 304 and the return catheter 302 is an inlet lumen 318 defined bya supply catheter 310. The inlet lumen 318 may be used to deliver aworking fluid to the interior of the heat transfer element 304. Theoutlet lumen 320 may be used to return or exhaust the working fluid fromthe heat transfer element 304. As above, their respective functions mayalso be reversed. The radius of the return catheter may be greater orless (in the case where their roles are reversed) than the radius of thesupply catheter. The working fluid may be used to heat or cool the heattransfer element which in turn heats or cools the fluid surrounding theheat transfer element.

A drug delivery catheter 312 defines the third lumen 316 and as shownmay be coaxial with the inlet lumen 318 and the outlet lumen 320. Ofcourse, the delivery catheter 312 may be also be off-axis or non-coaxialwith respect to the inlet lumen 318 and the outlet lumen 320.

For example, as shown in FIG. 16, the drug delivery catheter may be alumen 316′ within the return catheter and may be further defined by acatheter wall 312′. As another example, as shown in FIG. 17, the drugdelivery catheter may be a lumen 316″ adjacent to and parallel to thereturn catheter and may be further defined by a catheter wall 312″. Inan alternative embodiment, more than one lumen may be provided withinthe return catheter to allow delivery of several types of products,e.g., thrombolytics, saline solutions, etc. Of course, the supplycatheter may also be used to define the drug delivery catheter. The drugdelivery catheter may be substantially parallel to the return catheteror supply catheter or both, or may alternatively be at an oblique angle.The drug delivery catheter includes an outlet at a distal end thereof.The outlet may be distal or proximal of the distal end of the return orsupply catheters. The outlet may be directed parallel to the return andsupply catheters or may alternatively be directed transverse of thereturn and supply catheters.

The device may be inserted in a selected feeding vessel in the vascularsystem of a patient. For example, the device may be inserted in anartery which feeds a downstream organ or which feeds an artery which, inturn, feeds a downstream organ. In any of the embodiments of FIGS.15-17, the drug delivery catheter lumen may be used to deliver a drug,liquid, enzyme or other material to the approximate location of the heattransfer element. Such delivery may occur before, after, orcontemporaneous with heat transfer to or from the blood. For example,materials, e.g., drugs, liquids, enzymes, which operate at temperaturesother than normal body temperature may be used by first altering thelocal blood temperature with the heat transfer element and thendelivering the temperature specific material, e.g., atemperature-specific thrombolytic, which then operates at the alteredtemperature. Alternatively, such “third” lumens (with the supply andreturn catheters for the working fluid defining “first” and “second”lumens) may be used to remove particles, debris, or other desiredproducts from the blood stream.

FIGS. 18 and 19 show another embodiment of the invention that is relatedto the embodiment of FIG. 16. In this embodiment, several additionalsealed lumens are disposed in the return catheter. Some of the lumensmay be for drug delivery and others may be used to enhance mixing in amanner described below. The sealed lumens are in pressure communicationwith a supply of air to inflate the same. In FIG. 18, a return catheter302′ has one lumen 316′″C as shown for drug delivery. Another, lumen316′″I, is shown which may be employed to alter the geometry and shapeof the overall catheter. That is, inflating lumen 316′″I causes thelumen to expand in the same way that inflating a balloon causes it toexpand. In order to allow for the expansion, appropriately reducedreturn catheter wall thicknesses may be employed. Also, inflatablelumens 316′″A-B and 316′″D-N may be distributed in a substantiallysymmetric fashion around the circumference of the catheter for a uniforminflation if desired. Of course, less distortion under inflation mayoccur at or adjacent lumens such as 316′″C used for drug delivery, asthese do not inflate.

The inflatable lumens 316′″A-B and 316′″D-N may be caused to inflateunder influence of, e.g., an air compressor with a variable air deliveryflow. Rapid pulses of air may be used to inflate the lumens 316′″A-B and316′″D-N in a rapid and repeated fashion. By so doing, the outer wallsdefining these lumens move rapidly into and out of the bloodstreamaround the catheter, inducing turbulence. Preferably, the amplitude ofthe vibrations is large enough to move the outer walls defining thelumens out of the boundary layer and into the free stream of blood. Thiseffect produces mixing which is used to enhance heat transfer. As it isimportant to induce mixing primarily near the heat transfer element, thearea of appropriate wall thickness to allow for inflation need only beat, near, or adjacent the portion of the return catheter exterior walladjacent the heat transfer element. In other words, the return catheterwall only requires substantial reduction near the heat transfer element.The remainder of the catheter wall may remain thick for strength anddurability.

The supply catheter 310 may be constructed such that the same does notcontact the interior of the distal end 308 of the heat transfer element,which may cause a subsequent stoppage of flow of the working fluid. Suchconstruction may be via struts located in the return catheter 302 thatextend radially inwards and secure the supply catheter 310 fromlongitudinal translations. Alternatively, struts may extendlongitudinally from the distal end of the supply catheter 310 and holdthe same from contacting the heat transfer element. This construction issimilar to strut 112 shown in FIG. 11.

FIG. 20 shows an alternate method of accomplishing this goal. In FIG.20, a heat transfer element 304′ has an orifice 326 at a distal end 308.A supply catheter 310′ is equipped with a drag delivery catheter 312′extending coaxially therein. The drug delivery catheter 312 may beformed of a solid material integral with supply catheter 310′, or thetwo may be bonded after being constructed of separate pieces, or the twomay remain separate during use, with a friction fit maintaining theirpositions with respect to each other. The supply catheter 310′ is “inposition” when a tapered portion 324 of the same is lodged in the hole326 in the heat transfer element 304′. The tapered portion 324 should belodged tightly enough to cause a strong friction fit so that workingfluid does not leak through the hole 326. However, the tapered portion324 should be lodged loosely enough to allow the supply catheter 310′ tobe removed from the heat transfer element 304′ if continued independentuse of the return catheter is desired.

The supply catheter 310′ has a plurality of outlets 322. Outlets 322 areprovided at points generally near or adjacent the distal end of thesupply catheter 310′. The outlets are provided such that, when thesupply catheter 310′ is in position, the outlets generally face the heattransfer element 304′. In this way, the working fluid, emerging from theoutlets 322, more directly impinges on the interior wall of the heattransfer element 304′. In particular, the working fluid exits theinterior of the supply catheter and flows into a volume defined by theexterior of the supply catheter and the interior of the heat transferelement.

For clarity, FIG. 20 does not show the invaginations on the interiorwall of the heat transfer element 304′. However, it will be understoodthat such invaginations may be present and may allow for enhanced heattransfer in combination with the emerging working fluid.

In the embodiments of FIGS. 10, 12, and 14-20, various types of catheterassemblies employing drug delivery catheters are described. In thoseembodiments, and particularly in the embodiments such as FIGS. 12, 15and 20, in which a distal end of the drug delivery catheter protrudessubstantially from the distal end of the remainder of the catheterassembly, a therapy may be performed in which the distal end of thecatheter is embedded into a clot to be dissolved. An enzyme solution,such as a warm or cool enzyme solution, may then be sent directly intothe clot to locally enhance the fibrinolytic activity.

In particular, the catheter may be placed as described above. In thisprocedure, however, the catheter is placed such that the tip of theprotruding drug delivery catheter touches, is substantially near, orbecomes embedded within the clot. An enzyme solution or other such drugis then delivered down the drug delivery catheter directly into the clotor into the volume of blood surrounding the clot. The enzyme solutionmay include tPA, streptokinase, urokinase, pro-urokinase, combinationsthereof, and may be heated to enhance fibrinolytic activity. In arelated embodiment, the solution may be a simple heated saline solution.The heated saline solution warms the clot, or the volume surrounding theclot, again leading to enhanced fibrinolytic activity.

In these procedures, it is advantageous to use embodiments of theinvention in which the distal tip of the drug delivery catheter issubstantially protruding, or is distal, from the remainder of thecatheter assembly. In this way, the distal tip may be disposed adjacentto or within a clot without being obstructed by the remainder of thecatheter assembly.

The heat transfer element 110 (FIG. 11) may employ any of the formsdisclosed above, as well as variations of these forms. For example, theheat transfer element 110 may employ alternating helical ridgesseparated by flexible joints, the ridges creating sufficient mixingand/or surface area to enhance heat transfer between a working fluid andblood in the artery or vein. Alternatively, the heat transfer element110 may be inflatable and may have sufficient surface area such that theheat transfer due to conduction alone is sufficient to provide therequisite heat transfer. Details of the heat transfer element 110 areomitted in FIG. 11 for clarity.

With reference to FIGS. 21 and 22, a catheter 400 constructed inaccordance with an alternative embodiment of the invention will now bedescribed. The catheter 400 includes an elongated catheter body 402 witha heat transfer element 404 located at a distal portion 406 of thecatheter body 402. The catheter 400 includes a multiple lumenarrangement 408 to deliver fluid to and from an interior 410 of the heattransfer element 404 and allow the catheter 400 to be placed into ablood vessel over a guidewire. The heat transfer element 404 includesturbulence-inducing invaginations 412 located on an exterior surface414. Similar invaginations may be located on an interior surface 416 ofthe heat transfer element 404, but are not shown for clarity. Further,it should be noted that the heat transfer element 404 is shown with onlyfour invaginations 412. Other embodiments may employ multiple elementsconnected by flexible joints or bellows as disclosed above. A singleheat transfer element is shown in FIG. 21 merely for clarity. In analternative embodiment of the invention, any of the other heat-transferelements described herein may replace heat transfer element 406.Alternatively, the multi-lumen arrangement may be used to deliver fluidto and from the interior of an operative element(s) other than aheat-transfer-element such as, but without limitation, a catheterballoon, e.g., a dilatation balloon.

The catheter 400 includes an integrated elongated multiple lumen membersuch as a bi-lumen member 418 having a first lumen member 420 and asecond lumen member 422. The bi-lumen member 418 has a substantiallyfigure-eight cross-sectional shape (FIG. 22) and an outer surface 419with the same general shape. The first lumen member 420 includes aninterior surface 424 defining a first lumen or guide wire lumen 426having a substantially circular cross-sectional shape. The interiorsurface 424 may be coated with a lubricious material to facilitate thesliding of the catheter 400 over a guidewire. The first lumen member 420further includes a first exterior surface 428 and a second exteriorsurface 430. The first lumen 426 is adapted to receive a guide wire forplacing the catheter 400 into a blood vessel over the guidewire in awell-known manner.

In FIGS. 21 and 22, the guide wire lumen 426 is not coaxial with thecatheter body 402. In an alternative embodiment of the invention, theguide wire lumen 426 may be coaxial with the catheter body 402.

The second lumen member 422 includes a first interior surface 432 and asecond interior surface 434, which is the same as the second exteriorsurface 430 of the first lumen member 420, that together define a secondlumen or supply lumen 436 having a substantially luniformcross-sectional shape. The second lumen member 422 further includes anexterior surface 438. The second lumen 436 has a cross-sectional areaA₂. The second lumen 436 is adapted to supply working fluid to theinterior of the heat transfer element 404 to provide temperature controlof a flow or volume of blood in the manner described above.

The second lumen member 422 terminates short of a distal end 440 of thecatheter 400, leaving sufficient space for the working fluid to exit thesupply lumen 436 so it can contact the interior surface 416 of the heattransfer element 404 for heat transfer purposes.

Although the second lumen member 422 is shown as a single supply lumenterminating adjacent the distal end 440 of catheter 400 to deliverworking fluid at the distal end of the catheter 200, with reference toFIG. 23, in an alternative embodiment of the invention, a single supplylumen member 435 may include one or more outlet openings 437 adjacentthe distal end 440 of the catheter 400 and one or more outlet openings439 adjacent a mid-point along the interior length of the heat transferelement 404. This arrangement improves the heat transfer characteristicsof the heat-transfer element 404 because fresh working fluid at the sametemperature is delivered separately to each segment 22, 24 of theinterior of the heat-transfer element 404 instead of in series.

Although two heat transfer segments 22, 24 are shown, it will be readilyapparent that a number of heat transfer segments other than two, e.g.,one, three, four, etc., may be used.

It will be readily apparent to those skilled in the art that in anotherembodiment of the invention, in addition to the one or more openings 437in the distal portion of the heat transfer element 404, one or moreopenings at one or more locations may be located anywhere along theinterior length of the heat transfer element 404 proximal to the distalportion.

With reference to FIG. 24, in an alternative embodiment of theinvention, first and second supply lumen members 441, 443 definerespective first and second supply lumens 445, 447 for supplying workingfluid to the interior of the heat transfer element 404. The first supplylumen 441 terminates just short of the distal end 440 of the catheter400 to deliver working fluid at the distal portion of the heat transferelement 404. The second supply lumen 443 terminates short of the distalportion of the catheter 400, for example, at approximately a mid-lengthpoint along the interior of the heat transfer element 404 for deliveringworking fluid to the second heat transfer segment 22. In an alternativeembodiment of the invention, the second lumen member 443 may terminateanywhere along the interior length of the heat transfer element 404proximal to the distal portion of the heat transfer element 404.Further, a number of supply lumens 443 greater than two may terminatealong the interior length of the heat transfer element 404 fordelivering a working fluid at a variety of points along the interiorlength of the heat transfer element 404.

With reference back to FIGS. 21 and 22, the bi-lumen member 418 ispreferably extruded from a material such as polyurethane or Pebax. In anembodiment of the invention, the bi-lumen member is extrudedsimultaneously with the catheter body 402. In an alternative embodimentof the invention, the first lumen member 420 and second lumen member 422are formed separately and welded or fixed together.

A third lumen or return lumen 442 provides a convenient return path forworking fluid. The third lumen 442 is substantially defined by theinterior surface 416 of the heat transfer element 404, an interiorsurface 444 of the catheter body 402, and the exterior surface 419 ofthe bi-lumen member 418. The inventors have determined that the workingfluid pressure drop through the lumens is minimized when the third lumen442 has a hydraulic diameter D₃ that is equal to 0.75 of the hydraulicdiameter D₂ of the second lumen 436. However, the pressure drop thatoccurs when the ratio of the hydraulic diameter D₃ to the hydraulicdiameter D₂ is substantially equal to 0.75 , i.e., 0.75±0.10, workswell. For flow through a cylinder, the hydraulic diameter D of a lumenis equal to four times the cross-sectional area of the lumen divided bythe wetted perimeter. The wetted perimeter is the total perimeter of theregion defined by the intersection of the fluid path through the lumenand a plane perpendicular to the longitudinal axis of the lumen. Thewetted perimeter for the return lumen 442 would include an inner wettedperimeter (due to the outer surface 419 of the bi-lumen member 418) andan outer wetted perimeter (due to the interior surface 444 of thecatheter body 402). The wetted perimeter for the supply lumen 436 wouldinclude only an outer wetted perimeter (due to the first and secondinterior surfaces 432, 434 of the bi-lumen member 418). Thus, the wettedperimeter for a lumen depends on the number of boundary surfaces thatdefine the lumen.

The third lumen 442 is adapted to return working fluid delivered to theinterior of the heat transfer element 404 back to an external reservoiror the fluid supply for recirculation in a well-known manner.

In an alternative embodiment, the third lumen 442 is the supply lumenand the second lumen 436 is the return lumen. Accordingly, it will bereadily understood by the reader that adjectives such as “first,”“second,” etc. are used to facilitate the reader's understanding of theinvention and are not intended to limit the scope of the invention,especially as defined in the claims.

In a further embodiment of the invention, the member 418 may include anumber of lumens other than two such as, for example, 1, 3, 4, 5, etc.Additional lumens may be used as additional supply and/or return lumens,for other instruments, e.g., imaging devices, or for other purposes,e.g., inflating a catheter balloon or delivering a drug.

Heating or cooling efficiency of the heat transfer element 404 isoptimized by maximizing the flow rate of working fluid through thelumens 436, 442 and minimizing the transfer of heat between the workingfluid and the supply lumen member. Working fluid flow rate is maximizedand pressure drop minimized in the present invention by having the ratioof the hydraulic diameter D₃ of the return lumen 442 to the hydraulicdiameter D₂ of the supply lumen 436 equal to 0.75. However, a ratiosubstantially equal to 0.75, i.e., 0.75±10-20%, is acceptable. Heattransfer losses are minimized in the supply lumen 436 by minimizing thesurface area contact made between the bi-lumen member 418 and theworking fluid as it travels through the supply lumen member. The surfacearea of the supply lumen member that the supplied working fluid contactsis much less than that in co-axial or concentric lumens used in the pastbecause the supplied working fluid only contacts the interior of onelumen member compared to contacting the exterior of one lumen member andthe interior of another lumen member. Thus, heat transfer losses areminimized in the embodiments of the supply lumen in the multiple lumenmember 418 of the present invention.

It will be readily apparent to those skilled in the art that the supplylumen 436 and the return lumen. 442 may have cross-sectional shapesother than those shown and described herein and still maintain thedesired hydraulic diameter ratio of substantially 0.75. With referenceto FIGS. 25 and 26, an example of a catheter 400 including a supplylumen and a return lumen constructed in accordance with an alternativepreferred embodiment of the invention, where the hydraulic diameterratio of the return lumen to the supply lumen is substantially equal to0.75 is illustrated. It should be noted, the same elements as thosedescribed above with respect to FIGS. 21 and 22 are identified with thesame reference numerals and similar elements are identified with thesame reference numerals, but with a (′) suffix.

The catheter 400 illustrated in FIGS. 25 and 26 includes a multiplelumen arrangement 408′ for delivering working fluid to and from aninterior 410 of the heat transfer element 404 and allowing the catheterto be placed into a blood vessel over a guide wire. The multiple lumenarrangement 408′ includes a bi-lumen member 418′ with a slightlydifferent construction from the bi-lumen member 418 discussed above withrespect to FIGS. 21 and 22. Instead of an outer surface 419 that isgenerally figure-eight shaped, the bi-lumen member 418′ has an outersurface 419′ that is circular. Consequently, the third lumen 442′ has anannular cross-sectional shape.

As discussed above, maintaining the hydraulic diameter ratio of thereturn lumen 436′ to the supply lumen 442′ substantially equal to 0.75maximizes the working fluid flow rate through the multiple lumenarrangement 408′.

In addition, the annular return lumen 442′ enhances the convective heattransfer coefficient within the heat transfer element 404, especiallyadjacent an intermediate segment or bellows segment 449. Working fluidflowing through the annular return lumen 442′, between the outer surface419′ of the bi-lumen member 418′ and the inner surface 416 of the heattransfer element, encounters a restriction 450 caused by the impingementof the bellows section 449 into the flow path. Although the impingementof the bellows section 449 is shown as causing the restriction 450 inthe flow path of the return lumen 442′, in an alternative embodiment ofthe invention, the bi-lumen member 418′ may create the restriction 450by being thicker in this longitudinal region of the bilumen member 418′.The distance between the bi-lumen member 418′ and the bellows section449 is such that the characteristic flow resulting from a flow ofworking fluid is at least of a transitional nature.

For a specific working fluid flux or flow rate (cc/sec), the mean fluidvelocity through the bellows section restriction 450 will be greaterthan the mean fluid velocity obtained through the annular return lumen442′ in the heat transfer segment 22, 24 of the heat transfer element404. Sufficiently high velocity through the bellows section restriction450 will result in wall jets 451 directed into the interior portion 416of the heat transfer segment 22. The wall jets 451 enhance the heattransfer coefficient within the helical heat transfer segment 22 becausethey enhance the mixing of the working fluid along the interior of thehelical heat transfer segment 22. Increasing the velocity of the jets451 by increasing the working fluid flow rate or decreasing the size ofthe restriction 450 will result in a transition closer to the jet exitand greater mean turbulence intensity throughout the helical heattransfer segment 22. Thus, the outer surface 419′ of the bi-lumen member418′, adjacent the bellows 449, and the inner surface of the bellows 449form means for further enhancing the transfer of heat between the heattransfer element 404 and the working fluid, in addition to that causedby the interior portion 416 of the helical heat transfer segment 22.

In an alternative embodiment of the invention, as described above, theheat transfer element may include a number of heat transfer segmentsother than two, i.e., 1, 3, 4, etc., with a corresponding number ofintermediate segments, i.e., the number of heat transfer segments minusone.

The embodiment of the multiple lumen arrangement 418 discussed withrespect to FIGS. 21 and 22 would not enhance the convective heattransfer coefficient as much as the embodiment of the multiple lumenarrangement 418′ discussed with respect to FIGS. 25 and 26 becauseworking fluid would preferentially flow through the larger areas of thereturn lumen 442, adjacent the junction of the first lumen member 420and second lumen member 422. Thus, high-speed working fluid would havemore contact with the outer surface 419 of the bilumen member 418 andless contact with the interior portion of 416 heat transfer element 404.In contrast, the annular return lumen 442′ of the multiple lumenarrangement 418′ causes working fluid flow to be axisymmetric so thatsignificant working fluid flow contacts all areas of the helical segmentequally.

The invention has been described with respect to certain embodiments. Itwill be clear to one of skill in the art that variations of theembodiments may be employed in the method of the invention. Accordingly,the invention is limited only by the scope of the appended claims.

What is claimed is:
 1. A device for heating or cooling a surroundingfluid in a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior; an elongated supply lumen having across-sectional area located within the catheter body and adapted todeliver a working fluid to the interior of the heat transfer element; anelongated return lumen having a cross-sectional area located within thecatheter body and adapted to return a working fluid from the interior ofthe heat transfer element; and the ratio of the hydraulic diameter ofthe return lumen to the hydraulic diameter of the supply lumen beingsubstantially equal to 0.75.
 2. The device of claim 1, wherein thesupply lumen is disposed substantially within the return lumen.
 3. Thedevice of claim 1, wherein one of the supply lumen and return lumen hasa cross-sectional shape that is substantially luniform.
 4. The device ofclaim 1, wherein one of the supply lumen and the return lumen has across-sectional shape that is annular.
 5. The device of claim 1, whereinsaid heat transfer element includes an interior portion adapted toinduce mixing of the working fluid and means for further enhancingmixing of said working fluid.
 6. The device of claim 1, wherein the heattransfer element includes an interior distal portion, the supply lumenincludes first means for delivering working fluid to the interior distalportion of the heat transfer element and second means for deliveringworking fluid to the interior of the heat transfer element at one ormore points point proximal to the distal portion of the heat transferelement.
 7. The device of claim 1, wherein the supply lumen has ageneral cross-sectional shape and the return lumen has a generalcross-sectional shape different from the general cross-sectional shapeof the supply lumen.
 8. The device of claim 1, wherein said catheterassembly includes an integrated elongated bi-lumen member including afirst lumen adapted to receive a guide wire and a second lumen, thesecond lumen comprising either said supply lumen or said return lumen.9. The device of claim 8, wherein said bi-lumen member has across-sectional shape that is substantially in the shape of a figureeight.
 10. The device of claim 8, wherein said first lumen has across-sectional shape that is substantially circular and the secondlumen has a cross-sectional shape that is annular.
 11. The device ofclaim 1, wherein the heating element includes means for inducing mixingin a surrounding fluid.
 12. A catheter assembly capable of insertioninto a selected blood vessel in the vascular system of a patient,comprising: an elongated catheter body including an operative elementhaving an interior at a distal portion of the catheter body; anelongated supply lumen adapted to deliver a working fluid to theinterior of said distal portion and having a hydraulic diameter; anelongated return lumen adapted to return a working fluid from theinterior of said operative element and having a hydraulic diameter; andthe ratio of the hydraulic diameter of the return lumen to the hydraulicdiameter of the supply lumen being substantially equal to 0.75.
 13. Thecatheter assembly of claim 12, wherein the supply lumen is disposedsubstantially within the return lumen.
 14. The catheter assembly ofclaim 12, wherein one of the supply lumen and return lumen has across-sectional shape that is substantially luniform.
 15. The catheterassembly of claim 12, wherein one of the supply lumen and the returnlumen has a cross-sectional shape that is annular.
 16. The catheterassembly of claim 12, wherein the supply lumen has a generalcross-sectional shape and the return lumen has a general cross-sectionalshape different from the general cross-sectional shape of the supplylumen.
 17. The catheter assembly of claim 12, wherein said catheterassembly includes an integrated bi-lumen member including a first lumenadapted to receive a guide wire and a second lumen, the second lumencomprising either said supply lumen or said return lumen.
 18. Thecatheter assembly of claim 17, wherein said bi-lumen member has across-sectional shape that is substantially in the shape of a figureeight.
 19. The catheter assembly of claim 17, wherein said first lumenhas a cross-sectional shape that is substantially circular and thesecond lumen has a cross-sectional shape that is substantially luniform.20. The catheter assembly of claim 12, wherein said operative elementincludes a heat transfer element adapted to transfer heat to or fromsaid working fluid.
 21. The catheter assembly of claim 20, wherein saidheat transfer element includes means for inducing mixing in asurrounding fluid.
 22. The catheter assembly of claim 12, wherein saidoperative element includes a catheter balloon adapted to be inflatedwith said working fluid.
 23. A device for heating or cooling asurrounding fluid in a blood vessel, comprising: an elongated catheterbody including an internal wall; a heat transfer element located at adistal portion of the catheter body and including an interior; anintegrated elongated bi-lumen member located within said catheter bodyand including an external wall, a first lumen adapted to receive a guidewire and a second lumen, the second lumen comprising either a supplylumen to deliver a working fluid to an interior of the heat transferelement or a return lumen to return a working fluid from the interior ofthe heat transfer element; and a third lumen comprising either a supplylumen to deliver a working fluid to an interior of the heat transferelement or a return lumen to return a working fluid from the interior ofthe heat transfer element, the third lumen substantially defined by saidinternal wall of the catheter body and the exterior wall of the bi-lumenmember.
 24. A device for heating or cooling a surrounding fluid in ablood vessel, comprising: an elongated catheter body; a heat transferelement located at a distal portion of the catheter body and includingan interior; an integrated elongated bi-lumen member located within saidcatheter body and including a first lumen adapted to receive a guidewire and a second lumen, the second lumen comprising either a supplylumen to deliver a working fluid to an interior of the heat transferelement or a return lumen to return a working fluid from the interior ofthe heat transfer element; and a third lumen comprising either a supplylumen to deliver a working fluid to an interior of the heat transferelement or a return lumen to return a working fluid from the interior ofthe heat transfer element, the bi-lumen member disposed substantiallywithin the third lumen.
 25. A device for heating or cooling asurrounding fluid in a blood vessel, comprising: an elongated catheterbody; a heat transfer element located at a distal portion of thecatheter body and including an interior; an integrated elongatedbi-lumen member located within said catheter body and including a firstlumen adapted to receive a guide wire and a second lumen, the secondlumen comprising either a supply lumen to deliver a working fluid to aninterior of the heat transfer element or a return lumen to return aworking fluid from the interior of the heat transfer element; and athird lumen comprising either a supply lumen to deliver a working fluidto an interior of the heat transfer element or a return lumen to returna working fluid from the interior of the heat transfer element the thirdlumen having a cross-sectional shape that is annular.
 26. A device forheating or cooling a surrounding fluid in a blood vessel, comprising: anelongated catheter body; a heat transfer element located at a distalportion of the catheter body and including an interior portion adaptedto induce mixing of the working fluid and means for further enhancingmixing of said working fluid; an integrated elongated bi-lumen memberlocated within said catheter body and including a first lumen adapted toreceive a guide wire and a second lumen, the second lumen comprisingeither a supply lumen to deliver a working fluid to the interior portionof the heat transfer element or a return lumen to return a working fluidfrom the interior portion of the heat transfer element; and a thirdlumen comprising either a supply lumen to deliver a working fluid to theinterior portion of the heat transfer element or a return lumen toreturn a working fluid from the interior portion of the heat transferelement.
 27. A device for heating or cooling a surrounding fluid in ablood vessel, comprising: an elongated catheter body; a heat transferelement located at a distal portion of the catheter body and includingan interior and an interior distal portion; an integrated elongatedbi-lumen member located within said catheter body and including a firstlumen adapted to receive a guide wire and a second lumen, the secondlumen comprising either a supply lumen to deliver a working fluid to aninterior of the heat transfer element or a return lumen to return aworking fluid from the interior of the heat transfer element; and athird lumen comprising either a supply lumen to deliver a working fluidto an interior of the heat transfer element or a return lumen to returna working fluid from the interior of the heat transfer element, thesupply lumen including first means for delivering working fluid to theinterior distal portion of the heat transfer element and second meansfor delivering working fluid to the interior of the heat transferelement at one or more points proximal to the distal portion of the heattransfer element.
 28. A device for heating or cooling a surroundingfluid in a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior; an integrated elongated bi-lumen member locatedwithin said catheter body and including a first lumen adapted to receivea guide wire and a second lumen, the second lumen comprising either asupply lumen to deliver a working fluid to an interior of the heattransfer element or a return lumen to return a working fluid from theinterior of the heat transfer element, the second lumen having a generalcross-sectional shape; and a third lumen comprising either a supplylumen to deliver a working fluid to an interior of the heat transferelement or a return lumen to return a working fluid from the interior ofthe heat transfer element, the third lumen having a generalcross-sectional shape different from the general cross-sectional shapeof the second lumen.
 29. A device for heating or cooling a surroundingfluid in a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior; an integrated elongated bi-lumen member locatedwithin said catheter body and including a first lumen adapted to receivea guide wire and a second lumen, the second lumen comprising either asupply lumen to deliver a working fluid to an interior of the heattransfer element or a return lumen to return a working fluid from theinterior of the heat transfer element, the bi-lumen member having across-sectional shape that is substantially in the shape of a figureeight; and a third lumen comprising either a supply lumen to deliver aworking fluid to an interior of the heat transfer element or a returnlumen to return a working fluid from the interior of the heat transferelement.
 30. A device for heating or cooling a surrounding fluid in ablood vessel, comprising: an elongated catheter body; a heat transferelement located at a distal portion of the catheter body and includingan interior and means for inducing mixing in a surrounding fluid; anintegrated elongated bi-lumen member located within said catheter bodyand including a first lumen adapted to receive a guide wire and a secondlumen, the second lumen comprising either a supply lumen to deliver aworking fluid to an interior of the heat transfer element or a returnlumen to return a working fluid from the interior of the heat transferelement; and a third lumen comprising either a supply lumen to deliver aworking fluid to an interior of the heat transfer element or a returnlumen to return a working fluid from the interior of the heat transferelement.
 31. The catheter assembly of claim 30, wherein the catheterbody includes an internal wall and the integrated bi-lumen memberincludes an exterior wall, the third lumen substantially defined by saidinternal wall of the catheter body and the exterior wall of the bi-lumenmember.
 32. A catheter assembly capable of insertion into a selectedblood vessel in the vascular system of a patient, including: anelongated catheter body including an operative element having aninterior at a distal portion of the catheter body; an integratedelongated bi-lumen member located within said catheter body andincluding a first lumen adapted to receive a guide wire and a secondlumen, the second lumen comprising either a supply lumen to deliver aworking fluid to the interior of the operative element or a return lumento return a working fluid from the interior of the operative element;and a third lumen within said catheter body and comprising either asupply lumen to deliver a working fluid to an interior of the operativeelement or a return lumen to return a working fluid from the interior ofthe operative element, the bi-lumen member disposed substantially withinthe third lumen.
 33. A catheter assembly capable of insertion into aselected blood vessel in the vascular system of a patient, including: anelongated catheter body including an operative element having aninterior at a distal portion of the catheter body; an integratedelongated bi-lumen member located within said catheter body andincluding a first lumen adapted to receive a guide wire and a secondlumen, the second lumen comprising either a supply lumen to deliver aworking fluid to the interior of the operative element or a return lumento return a working fluid from the interior of the operative element;and a third lumen within said catheter body and comprising either asupply lumen to deliver a working fluid to an interior of the operativeelement or a return lumen to return a working fluid from the interior ofthe operative element, said third lumen having a cross-sectional shapethat is annular.
 34. A catheter assembly capable of insertion into aselected blood vessel in the vascular system of a patient, including: anelongated catheter body including an operative element having aninterior at a distal portion of the catheter body; an integratedelongated bi-lumen member located within said catheter body andincluding a first lumen adapted to receive a guide wire and a secondlumen, the second lumen comprising either a supply lumen to deliver aworking fluid to the interior of the operative element or a return lumento return a working fluid from the interior of the operative element,the second lumen having a general cross-sectional shape; and a thirdlumen within said catheter body and comprising either a supply lumen todeliver a working fluid to an interior of the operative element or areturn lumen to return a working fluid from the interior of theoperative element, the third lumen having a general cross-sectionalshape different from the general cross-sectional shape of the secondlumen.
 35. A catheter assembly capable of insertion into a selectedblood vessel in the vascular system of a patient, including: anelongated catheter body including an operative element having aninterior at a distal portion of the catheter body; an integratedelongated bi-lumen member located within said catheter body andincluding a first lumen adapted to receive a guide wire and a secondlumen, the second lumen comprising either a supply lumen to deliver aworking fluid to the interior of the operative element or a return lumento return a working fluid from the interior of the operative element,said bi-lumen member having a cross-sectional shape that issubstantially in the shape of a figure eight; and a third lumen withinsaid catheter body and comprising either a supply lumen to deliver aworking fluid to an interior of the operative element or a return lumento return a working fluid from the interior of the operative element.36. A device for heating or cooling a surrounding fluid in a bloodvessel, comprising: an elongated catheter body; a heat transfer elementincluding at least a first heat transfer segment and a second heattransfer segment located at a distal portion of the catheter body andincluding an interior distal portion and an interior portion; and afirst elongated supply lumen located within the catheter body andterminating at the interior distal portion of the heat transfer elementinto first means for delivering working fluid to the interior distalportion of the heat transfer element; and a second elongated supplylumen located within the catheter body and terminating at a pointproximal to the distal portion of the heat transfer element into secondmeans for delivering working fluid to the interior portion of the heattransfer element at a point proximal to the distal portion of the heattransfer element.
 37. The device of claim 36, wherein the first workingfluid delivering means is adapted to deliver working fluid to theinterior distal portion of the heat transfer element and the secondworking fluid delivering means is adapted to deliver working fluid tothe interior portion of the heat transfer element near a midpoint of theheat transfer element.
 38. A device for heating or cooling a surroundingfluid in a blood vessel, comprising: an elongated catheter body; a heattransfer element including at least a first heat transfer segment and asecond heat transfer segment located at a distal portion of the catheterbody and including an interior distal portion and an interior portion;and a first elongated supply lumen located within the catheter body andterminating at the interior distal portion of the first heat transfersegment into first means for delivering working fluid to the interior ofthe first heat transfer segment; and a second elongated supply lumenlocated within the catheter body and terminating at a point proximal tothe distal portion of the heat transfer element into second means fordelivering working fluid to the interior portion of the second heattransfer segment.
 39. The device of claim 38, wherein the second workingfluid delivering means is adapted to deliver working fluid to theinterior portion of the heat transfer element near a midpoint of theheat transfer element.
 40. A device for heating or cooling a surroundingfluid in a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior portion adapted to induce mixing of a workingfluid to effect heat transfer between the heat transfer element andworking fluid, the heat transfer element including at least a first heattransfer segment, a second heat transfer segment, and an intermediatesegment between the first heat transfer segment and the second heattransfer segment; an elongated supply lumen member located within thecatheter body and adapted to deliver the working fluid to the interiorof the heat transfer element, said supply lumen member including acircular outer surface; an elongated return lumen defined in part by theouter surface of the supply lumen member and the interior portion of theheat transfer element and adapted to return the working fluid from theinterior of the heat transfer element; and wherein the distance betweenthe interior portion of the heat transfer element and the outer surfaceof the supply lumen member adjacent the intermediate segment is lessthan the distance between the interior portion of the heat transferelement and the outer surface of the supply lumen member adjacent thefirst heat transfer segment.
 41. The device of claim 40, wherein thedistance between the interior portion of the heat transfer element andthe outer surface of the supply lumen member adjacent the intermediatesegment is such that the characteristic flow resulting from a flow ofworking fluid is at least of a transitional nature.
 42. The device ofclaim 40, wherein the intermediate segment includes an interior diameterthat is less than the interior diameter of the first heat transfersegment or the second heat transfer segment.
 43. The device of claim 40,wherein the supply lumen member includes an outer diameter adjacent theintermediate segment that is greater than its outer diameter adjacentthe first heat transfer segment or the second heat transfer segment. 44.The device of claim 40, wherein the supply lumen member comprises amultiple-lumen member.
 45. The device of claim 40, wherein the supplylumen member includes a supply lumen having a hydraulic diameter and thereturn lumen has a hydraulic diameter substantially equal to 0.75 of thehydraulic diameter of the supply lumen.
 46. The device of claim 40,wherein the intermediate segment includes a flexible bellows joint. 47.The device of claim 40, wherein the intermediate segment includes aflexible tube.
 48. A device for heating or cooling a surrounding fluidin a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior portion with first means for mixing a workingfluid to effect heat transfer between the heat transfer element andworking fluid; an elongated supply lumen member located within thecatheter body and adapted to deliver the working fluid to the interiorof the heat transfer element; an elongated return lumen member locatedwithin the catheter body and adapted to return the working fluid fromthe interior of the heat transfer element; and second means locatedwithin said heat transfer element for further enhancing mixing of saidworking fluid to effect further heat transfer between the heat transferelement and working fluid, said second means being different from saidfirst means.
 49. A device for heating or cooling a surrounding fluid ina blood vessel, comprising: an elongated catheter body; a heat transferelement located at a distal portion of the catheter body and includingan interior portion adapted to induce mixing of a working fluid toeffect heat transfer between the heat transfer element and workingfluid; an elongated supply lumen member located within the catheter bodyand adapted to deliver the working fluid to the interior of the heattransfer element, the supply lumen member including a multiple-lumenmember having a circular outer surface; an elongated return lumen memberlocated within the catheter body and adapted to return the working fluidfrom the interior of the heat transfer element; and means located withinsaid heat transfer element for further enhancing mixing of said workingfluid to effect further heat transfer between the heat transfer elementand working fluid.
 50. A device for heating or cooling a surroundingfluid in a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior portion adapted to induce mixing of a workingfluid to effect heat transfer between the heat transfer element andworking fluid; an elongated supply lumen member located within thecatheter body and adapted to deliver the working fluid to the interiorof the heat transfer element, the supply lumen member including a supplylumen having a hydraulic diameter; an elongated return lumen memberlocated within the catheter body and adapted to return the working fluidfrom the interior of the heat transfer element, the return lumen havinga hydraulic diameter substantially equal to 0.75 of the hydraulicdiameter of the supply lumen; and means located within said heattransfer element for further enhancing mixing of said working fluid toeffect further heat transfer between the heat transfer element andworking fluid.
 51. A device for heating or cooling a surrounding fluidin a blood vessel, comprising: an elongated catheter body; a heattransfer element located at a distal portion of the catheter body andincluding an interior portion adapted to induce mixing of a workingfluid to effect heat transfer between the heat transfer element andworking fluid; an elongated supply lumen member located within thecatheter body and adapted to deliver the working fluid to the interiorof the heat transfer element, the supply lumen member including amultiple-lumen member having a circular outer surface; an elongatedreturn lumen member located within the catheter body and adapted toreturn the working fluid from the interior of the heat transfer element;and a mixing-enhancing mechanism located within said heat transferelement and adapted to further mix said working fluid to effect furtherheat transfer between the heat transfer element and working fluid.
 52. Adevice for heating or cooling a surrounding fluid in a blood vessel,comprising: an elongated catheter body; a heat transfer element locatedat a distal portion of the catheter body and including an interiorportion adapted to induce mixing of a working fluid to effect heattransfer between the heat transfer element and working fluid; anelongated supply lumen member located within the catheter body andadapted to deliver the working fluid to the interior of the heattransfer element, the supply lumen member including a supply lumenhaving a hydraulic diameter; an elongated return lumen member locatedwithin the catheter body and adapted to return the working fluid fromthe interior of the heat transfer element, the return lumen having ahydraulic diameter substantially equal to 0.75 of the hydraulic diameterof the supply lumen; and a mixing-enhancing mechanism located withinsaid heat transfer element and adapted to further mix said working fluidto effect further heat transfer between the heat transfer element andworking fluid.
 53. A method of heating or cooling a surrounding fluid ina blood vessel, comprising: providing a device for heating or cooling asurrounding fluid in a blood vessel within the blood stream of a bloodvessel, the device including an elongated catheter body, a heat transferelement located at a distal portion of the catheter body and includingan interior portion with first means for mixing a working fluid toeffect heat transfer between the heat transfer element and workingfluid, an elongated supply lumen member located within the catheter bodyand adapted to deliver the working fluid to the interior of the heattransfer element, an elongated return lumen member located within thecatheter body and adapted to return the working fluid from the interiorof the heat transfer element, and second means located within said heattransfer element for further enhancing mixing of said working fluid toeffect further heat transfer between the heat transfer element andworking fluid, said second means being different from said first means;causing a working fluid to flow to and along the interior portion of theheat transfer element of the device using the supply lumen and returnlumen; facilitating the transfer of heat between the working fluid andthe heat transfer element by effecting mixing of the working fluid withthe first means for mixing the working fluid; facilitating additionaltransfer of heat between the working fluid and the heat transfer elementby effecting further mixing of the working fluid within the interiorportion with the second means for further enhancing mixing of theworking fluid; causing heat to be transferred between the blood streamand the heat transfer element without ablating tissue by the heattransferred between the heat transfer element and working fluid.